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COPYRIGHT DEPOSIT, 



ANALYSIS OF MILK 



AND 



MILK PRODUCTS 



LEFFMANN 



SANITARY RELATIONS OF THE 
COAL-TAR COLORS 

BY 
THEODORE WEYL 

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HENRY LEFFMANN 
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EXAMINATION OF WATER 

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ORGANIC CHEMISTRY 

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SELECT METHODS IN FOOD 
ANALYSIS 

BY 

Henry Leffmann and William Beam 

Second Edition, Revised 

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I Plate and 54 Illustrations 



ALLEN'S COMMERCIAL ORGANIC 
ANALYSIS 

VOLUME 8 CONTAINS: 
Methods of Analysis of Milk and Milk-Prod- 
ucts, Meat and Meat- Products, Proteins, Pro- 
teoids, Fibroids and Enzyms. 
8vo. 696 Pages. $5.00 net 



ANALYSIS OF MILK 



AND 



MILK PRODUCTS 



BY 

HENRY LEFFMANN, M. D. 

PROFESSOR OF CHEMISTRY IN THE WOMAN'S MEDICAL COLLEGE OF 

PENNSYLVANIA AND IN THE WAGNER FREE INSTITUTE OF 

SCIENCE OF PHILADELPHIA; PATHOLOGICAL CHEMIST 

TO JEFFERSON MEDICAL COLLEGE HOSPITAL 



FOURTH EDITION, REVISED AND ENLARGED 
WITH ILLUSTRATIONS 



THE FIRST TWO EDITIONS OF THIS WORK WERE 
PREPARED AND ISSUED UNDER THE JOINT AUTHOR- 
SHIP OF HENRY LEFFMANN AND WILLIAM BEAM 



PHILADELPHIA 

P. BLAKISTON'S SON & CO. 

1012 WALNUT STREET 






Copyright, 191 5, by Henry Leffmann 



f z;?!' 



THB MAFXiB FKISSB TORK PA 



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K.-f^ 



PREFACE 

This book is intended as a guide to the analysis 
of milk and milk products in the routine of the 
commercial and food-inspection laboratory. 
Only processes of practical value have been given, 
and nothing has been said as to the food value 
of milk and its products, nor concerning the ef- 
fects of the several adulterants that may be 
detected. 

A notable portion of the text has been taken 
from Volume 8 of the Fourth Edition of Allen's 
Commercial Organic Analysis, I am indebted to 
the courtesy of Messrs. P. Blakiston's Son & Co. 
for permission to use this matter. 

An interesting point is to be noted in the com- 
parison of this edition with the first, issued about 
a score of years ago in association with Dr. 
William Beam. In that, a considerable part of 
the material was derived from the publications 
of foreign workers; in the present, American in- 
vestigations form the basis of many of the im- 
portant processes. 

" Westward the star 0} empire takes its way.^^ 

H. L. 
Philadelphia. 



CONTENTS 

Milk. Page 

Analytic Data and Processes 1-64 

Milk Products. 

Cream 65-68 

Condensed Milk 69-8O 

Butter 81-96 

Cheese 97-109 

Fermented Milk Products 110-113 

Index 



Vll 



MILK 



ANALYTIC DATA 

Milk, the nutritive secretion of nursing mam- 
mals, contains water, fat, proteins, sugar, and 
mineral matter. Cow's milk is meant in all 
cases, unless otherwise stated. Milk as taken 
from the animal is generally termed "whole 
milk." 

Fat. — This occurs in globules varying from 
0.0015 mm. to 0.005 ^^- i^ diameter, in a 
condition which prevents spontaneous coales- 
cence. It is pecuHar among animal fats in 
containing a notable proportion of acid radicles 
with a small number of carbon atoms. 

Proteins. — The nature of the proteins of 
milk has been much discussed, but it is now 
generally conceded that there are at least three 
forms, casein, albumin, and globulin, the casein 
being present in by far the greatest amount, 
and the globulin as traces only. 

Casein. — Casein is probably in part in 
combination with phosphates. It is precipi- 



2 MILK 

tated by many substances, among which are 
acids, rennet, and magnesium sulfate, but not 
by heat. Acids precipitate it by breaking up 
the combination with phosphates. The action 
of rennet is complex and probably partly hy- 
hydrolytic, splitting the casein into several 
proteins, some of which are precipitated in 
the curd. Films of protein matter occur abun- 
dantly in milk, for which reason it is distinctly 
opaque, even when nearly all the fat has been 
removed by contrifugal action. 

The albumin of milk appears to be a distinct 
form, and is called lactalbumin. It is not 
precipitated by dilute acids, but is coagulated by 
heating to 70° — 75°. The proportion in cow's 
milk is usually from 0.35 to 0.50%, but col- 
ostrum may contain much larger proportions. 

Globulin is present only in minute amounts 
in normal milk, but colostrum may contain as 
much as 8%. It is coagulated on heating. 

Lactose. — This is a sugar peculiar to milk. 

Citric acid is a normal constituent of the milk 
of various animals. In human milk, the quantity 
is about 0.5 gram to 1000 c.c. ; in cow's milk, 
from I to 1.5 grams. It is not dependent on 
the citric acid present in the food. 

Enzyms. — Several enzyms occur in milk but 
they are chiefly known by effects and not as 
isolated substances. Some are proteolytic, others 



ANALYTIC DATA 3 

are oxydases, that is, decompose hydrogen per- 
oxid and carry oxygen over to other substances. 

Lecithin is also a usual ingredient of milk. 
Nerking and Haensel found a range in cows' 
milk from 0.03 to 0.11%. 

Mineral Matter.— The ash of milk contains 
calcium, magnesium, iron, potassium, and sodium 
as chlorids, carbonates, sulfates, and phos- 
phates. It does not exactly represent the salts 
present in milk. 

Richmond has determined the ratio of the 
ash to the soHds not fat in 135 samples of milk. 
This was found to range from 7.8 to 9.4%, 
but more usually from 7.8 to 8.5 (average 8.2) %. 
Many ashes were alkaline to turmeric, litmus, 
and phenolphthalein, the maximum alkalinity 
being 0.025% calculated as sodium carbonate. 

Human milk is notable for a low protein 
content hence the curd is less bulky and more 
friable than that from cows' milk. The milk 
of all animals is subject to modification by breed, 
climate, season, feed, housing, exercise, time 
of lactation, and in human beings (and possibly 
in some other animals) by psychic influences. 

As regards the proportion of proteins and 
lactose, milks of the mare and ass agree closely 
with human milk. 

Normal milk is an opaque white or yellowish- 
white fluid, with an odor recalling that of the 



4 MILK 

animal, and a faint sweet taste. The opacity 
is due largely but not entirely to the fat globules. 
The reaction of freshly drawn milk to litmus is 
usually alkaline, but is sometimes amphoteric; 
that is, it turns the red paper blue and the blue 
paper red. The sp. gr. varies between 1.027 
and 1.035. It usually undergoes a gradual 
augmentation (sometimes termed Recknagel's 
phenomenon) for a considerable time after the 
sample has been drawn. The increase may 
amount to two units (water being 1000). The 
sp. gr. becomes stationary in about five hours 
if the milk is maintained at a temperature 
below 15°, but at a higher temperature it may 
require twenty-four hours to acquire constancy. 
The change is not entirely dependent on the 
escape of gases. 

Unless collected with special care and under 
conditions of extreme cleanliness, milk always 
contains many bacteria, animal matter of an 
offensive character, such as epithelium, blood 
and pus cells, particles of feces, and soil. 

At ordinary temperature milk soon undergoes 
decomposition, by which the milk sugar is 
converted principally into lactic acid, and the 
proteins partly decomposed and partly coagu- 
lated. The liquid becomes sour and the fat is 
inclosed in the coagulated casein. In the initial 
stages of decomposition the proteins frequently 



ANALYTIC DATA 5 

undergo transformations into substances which 
are the cause of the violent poisonous effects 
occasionally produced by ice-cream and other' 
articles of food into the preparation of which 
milk enters. 

Boiling produces coagulation of the albumin, 
some caramelization of the sugar, and develops 
a greater facility of coalescence on the part of 
the fat globules. Enzyms are rendered inert 
and most microbes are killed. 

When milk is allowed to stand, some of the fat 
rises gradually and forms a rich layer, constituting 
cream. The proportion of cream depends on 
several conditions. The amount formed in a 
given time cannot be taken as a measure of the 
richness of the milk. Water added to milk 
causes a more rapid separation of the cream. 
Centrifugal action separates nearly all of the fat. 
The following figures, given by D'Hout as aver- 
ages, show this effect : 

Whole Separated i^„„.». 
Milk Milk <-Rkam 

Specific gravity 1032 1034 1015 

Total solids 14.10 9.6 26.98 

Sugar 4.70 5.05 3.32 

Casein 3.50 3 . 62 2 . 02 

Ash 0.79 0.78 0.58 

Fat 5.05 0.20 21.95 

Buttermilk is the residue after removal of the 
butter by churning. Vieth gives the following 
analyses : 



6 MILK 

Total p._ Solids not a^„ 

Solids ^^^ Fat ^^^ 

9.03 0.63 8.40 0.70 

8.02 0.65 7.37 1.29 

10.70 0.54 10.16 0.82 

Whey or Milk-serum is the liquid freed from 
curd after precipitation by rennet or acids. In 
most cases it contains a notable amount of 
proteins, as shown in the following analyses by 
Cochran : 

Milk Whey 

Total solids Solids not fat Total solids J^emoved 

927 9-13 6.62 2.51 

927 9.13 6.1 3.03 

14-05 8.35 6.62 2.33 

771 7-6i 5.98 1.63 

8.91 8.71 6.50 2.21 

The whey of any given milk has practically the 
same composition, whether taken from the 
original milk, skimmed milk, or cream. 

Average Proportion of Solids in Milk. — The 
most extensive data on this point are those 
obtained by Vieth. The total number of samples 
was 120,540. The averages of the entire series 
are as follows : 

Fat 4.1% 

Non-fatty solids 8.8% 

Total solids 12.9% 

Lythgoe gives a table of averages of composi- 
tion of 51 samples of genuine milk, each set of 



ANALYTIC DATA 



averages being deduced by analysis of lo samples. 
The following data are selected from this table. 
For explanation of the figures in the last column 
see page 42. 



Total 
Solids 

15-70 
15.00 
14.50 
14.00 
13 50 
13.00 
12.50 
12.00 

11.50 
11.00 

10.70 



Fat 

6.01 
5.62 
530 
4.78 
4.61 
4.24 
3-99 
3.45 
3-33 
3.02 
2.90 



Pro- 
teins 

4.13 
3-75 
3-6i 
351 
3-37 
3.17 
2.84 
2.88 
2.67 
2.64 
2.60 



Lac- 
tose 



•79 

.87 
.82 

•98 

■ n 

.86 

.94 
.96 
.80 
.63 
•49 



Ash 

0.77 
0.76 

0.77 
0.73 
0.75 
0.73 
0.73 
0.74 
0.70 
0.71 
0.71 



Solids 

NOT 

Fat 
9.69 
938 
9.20 
9.22 
8.89 
8.76 
8.51 
8.55 
8.17 
7.98 
7.80 



Refraction 
OF Copper 
Serum 20° 

38.1 
38.3 
38.3 
38.5 
38.1 

37-9 
38.0 

37-7 
37.3 
37.0 

36.4 



From these figures Lythgoe derives the rule 
that differences in proportion of solids not fat in 
unadulterated milks are principally due to dif- 
ferences in the amount of proteins. Lactose and 
ash are fairly constant. On these facts depend 
recently introduced methods of detecting water- 
ing milk, as will be pointed out later. 

Colostrum. — This is the secretion in the early 
stages of lactation, and differs from ordinary 
milk. It contains characteristic structures, 
known as colostrum corpuscles, and usually 
contains much less fat than fully developed 
milk, but a larger proportion of proteins. Colo- 
strum coagulates on boiling. Lactose is in small 
amount. 



ANALYTIC PROCESSES 

Specific Gravity. — The sp. gr. of milk rises 
gradually for some time after it has been drawn, 
and the determination is to be made only after 
this action has ceased. This will require about 
five hours after the milk is drawn, if it has been 
kept 15°, but at a higher temperature it will be 
necessary to allow at least twelve hours. For 
all other determinations the milk must be ana- 
lyzed as soon as possible. The following figures, 
published by Bevan, show that a considerable 
loss in total solids may occur in twenty-four 
hours : 

Total Solids Loss 
Evaporated immediately ... 1 1 • 73 

Evaporated after 24 hours, 10 -79 0-94 

Evaporated after 48 hours, 10,38 1.35 

Evaporated after 120 hours, 9.42 2,31 

The decomposition is very irregular, and it is 
not possible to determine, by estimation of the 
lactic acid or other products, the original compo- 
sition of the milk. 

Air-bubbles are held rather tenaciously by milk, 
and care must be taken in mixing, preparatory 
to taking the sp. gr., to avoid as far as possible 

8 



ANALYTIC PROCESSES 9 

the inclosure of the air, and to allow sufficient 
time for the escape of any bubbles that may be 
present. Sp. gr. is understood to be taken at 1 5 . 5° ; 
samples should be brought near to this. If at 
a few degrees above or below, it will suffice to 
make the determination at once and obtain the 
correct figure by reference to the annexed table. 
The sp. gr. of normal milk ranges between 
1.027 and 1.035. The figure alone does not 
indicate the character of the sample, but taken 
in conjunction with the figure for fat or for 
total solids, it is of value as a check on the 
results furnished by other determinations. 

The simplest method of determining sp. gr. is 
by the lactometer, a delicate and accurately gradu- 
ated hydrometer. The instrument must be im- 
mersed carefully so as not to wet the stem above 
the point at which it will rest. Its accuracy 
should be verified by immersion in distilled 
water at 15.5° and milks of known sp. gr. 

More accurate determinations may be made 
with a balance. A special form, the Westphal 
balance, is adapted to the determination of 
sp. gr. only, the weights being so arranged 
that a simple enumeration of them gives the 
gravity directly. The cheap forms of this in- 
strument are not satisfactory, but some made 
by German houses are excellent. The ordinary 



lO 



MILK 



Find the temperature of the milk in one of the horizontal lines 
and the sp. gr. in the first vertical column. In the same line 
with this and the temperature the correct figure is given. 



°F. 


50 


51 


52 


53 


54 


55 


56 


57 


58 


59 


60 


61 


62 


Sp.Gr. 




























21 


20.2 


20.3 


20.3 


20.4 


20.5 


20.6 


20.7 


20.8 


20.9 


20.9 


21.0 


21. 1 


21.2 


22 


21.2 


21.3 


21.3 


21.4 


21.5 


21.6 


21.7 


21.8 


21.9 


21.9 


22.0 


22.1 


22.2 


23 


22.2 


22.3 


22.3 


22.4 


22.5 


22.6 


22.7 


22.8 


22.8 


22.9 


23.0 


23.1 


23.2 


24 


23.2 


23-3 


23-3 


234 


23-5 


23.6 


23.6 


237 


23-8 


23-9 


24.0 


24.1 


24.2 


25 


24.1 


24,2 


24.3 


24.4 


24-5 


24.6 


24.6 


24.7 


24.8 


24.9 


25.0 


25.1 


25.2 


26 


25-1 


25.2 


25.2 


25-3 


25.4 


25.5 


25.6 


25.7 


25.8 


25-9 


26.0 


26.1 


26.2 


27 


26.1 


26.2 


26.2 


26.3 


26.4 


26.5 


26.6 


26.7 


26.8 


26,9 


27.0 


27.1 


27.3 


28 


27.0 


27.1 


27.2 


27.3 


27.4 


27.5 


27.6 


27.7 


27.8 


27.9 


28.0 


28.1 


28.3 


29 


28.0 


28.1 


28.2 


28.3 


28.4 


28.5 


28.6 


28.7 


28.8 


28.9 


29.0 


29.1 


293 


30 


29.0 


29.1 


29.1 


29.2 


29-3 


29.4 


29.6 


29.7 


29.8 


29.9 


300 


30.1 


30.3 


31 


29.9 


30.0 


30.1 


30.2 


30.3 


30.4 


30.5 


30.6 


30.8 


30.9 


31.0 


31.2 


31.2 


32 


30.9 


31.0 


311 


31.2 


31.3 


31.4 


31-5 


31.6 


31.7 


31-9 


32.0 


32.2 


32.3 


33 


31.8 


31-9 


32.0 


32.1 


32.3 


32.4 


32.5 


32,6 


32.7 


32.9 


33-0 


33.2 


33.3 


34 


32.7 


32.9 


33.0 


33.1 


33-2 


33.3 


33-5 


33.6 


33-7 


33-9 


34-0 


34-2 


34-3 


35 


33.6 


33.8 


33-9 


34-0 


34-2 


34.3 


34-5 


34-6 


34-7 


34-9 


35.0 


35-2 


35-3 


°C. 


lO.O 


10.5 


II. I 


11.6 


12.2 


12.7 


13.3 


13.8 


14.4 


15.0 


15-5 


16.1 


16.6 



analytic balance may also be used. A plummet 
consisting of a thick glass rod (or short sealed 
tube, weighted with mercury) of a bulk of about 
10 c.c. is suspended from the hook of the balance 
by means of fine platinum wire and the weight 
ascertained. It is then submerged in distilled 
water and the weight also noted. The water is 
contained in a narrow upright cylinder resting 



ANALYTIC PROCESSES 



II 



Find the temperature of the milk in one of the horizontal lines 
and the sp. gr. in the first vertical column. In the same 
line with this and the temperature the correct figure is given. 



63 


64 65 


66 


67 


68 


69 


70 


71 


72 


73 


74 


75 


21.3 


21.4 


21.5 


21.6 


21.7 


21.8 


22.0 


22.1 


22.2 


22.3 


22.4 


22.5 


22.6 


22.3 


22.4 


22.5 


22.6 


22.7 


22.8 


23.0 


23.1 


23.2 


233 


23.4 


23-5 


23.7 


233 


23.4 


23.5 


23.6 


23.7 


23.8 


24.0 


24.1 


24.2 


243 


24.4 


24.6 


24.7 


24.3 


24.4 


24-5 


24.6 


24.7 


24.9 


25.0 


25.1 


25.2 


25.3 


25.5 


25.6 


25.7 


25.3 


25-4 


25-5 


25.6 


25.7 


259 


26.0 


26.1 


26.2 


26.4 


26.5 


26.6 


26.8 


26.3 


26.5 


26.6 


26.7 


26.8 


27.0 


27.1 


27.2 


27-3 


27.4 


27-5 


27.7 


27.8 


27.4 


27.5 


27.6 


27.727.8 


28.0 


28.1 


28.2 


28.3 


28.4 


28.6 


28.7 


28.9 


28.4 


28.5 


28.6 


28.728.8 


29.0 


29.1 


29.2 


29.4 


29.5 


29.7 


29.8 


29.9 


29.4 


295 


29.6 


29.829.9 


30.1 


30.2 


303 


30.4 


30.5 


30.7 


30.9 


310 


30.4 


30.5 


30.7 


30.8 


30.9 


311 


31-2 


313 


31.5 


31.6 


31.8 


319 


32.1 


314 


31.5 


31.7 


31.8 


32.0 


32.2 


32.2 


32.4 


32.5 


32.6 


32.8 


32.0 


33- 1 


32.5 


32.6 


32.7 


32.9 


33.0 


33-2 


33-3 


33-4 


33.6 


33-7 


33-9 


23.0 


34.2 


33-5 


33-6 


33-8 


33-9 


340 


34-2 


34-3 


34-5 


34.6 


34-7 


34-9 


35.1 


35.2 


34-5 


34.6 


34-8 


34-9 


350 


35-2 


35-3 


35-5 


35.6 


35-8 


36.0 


36.1 


36.3 


35-5 


35-6 


35.8 


35-9 


36.1 


36.2 


36.4 


36.5 


36.7 


36.8 


370 


37.2 


37-3 


17.2 


17.7 


18.3 


18. 819. 4 


20.0 


20.5 


21. 1 


21.6 


22.2 


22.7 


233 


23.8 



on a bench or support above the scale pan. 
The loss of weight of the plummet is, of course, 
the weight of the bulk of water that it displaces. 
The sp. gr. of any sample can be determined by- 
weighing the plummet immersed in the sample 
and dividing the loss in weight by the loss in 
water. The quotient is the sp. gr. 

The ordinary pyknometer is not convenient 



12 MILK 

on account of the liability of the upper layer 
of the liquid to be richer in fat than the lower ; 
the overflow, therefore, does not represent the 
mixture. 

Total Solids. — This determination may often 
be made with sufficient accuracy for practical 
purposes by evaporating a measured volume 
(^- g'j 3 or 5 c.c.) in a shallow nickel dish from 5 
to 8 cm. in diameter. Nickel crucible-covers are 
suitable. The thin glass (Petri) dishes used for 
microbe culture are convenient. When greater 
accuracy is required, and especially when the 
ash is to be determined, platinum dishes are the 
most satisfactory, but owing to the present price 
of this metal, quartz dishes are now much used. 
Either the translucent or transparent quartz is 
suitable, the former being less expensive. 

Good results may be secured as follows : A flat 
dish, 3.5 cm. in diameter, with sides 0.5 cm. high, 
is provided with a thin fiat watch-glass cover 
that fits rather closely. The total weight of the 
cover and dish is noted. 2 or 3 c.c. of the sample 
are run into the dish from the pipet, the watch- 
glass placed on, and the weight taken as rapidly 
as possible. The glass prevents appreciable 
loss from evaporation during an ordinary weigh- 
ing. The cover is removed, the dish heated on 
the water-bath or in the water-oven, and weighed 
from time to time (with cover on it) until the 



ANALYTIC PROCESSES I3 

weight is sensibly constant. The percentage 
of residue can be easily calculated. About three 
hours may be required to secure constant weight. 

When high accuracy is not essential, it will 
suffice to measure the milk. Vieth advised a 
pipet graduated to deliver 5 grams, and found 
that, working with whole and skimmed milk, 
under the ordinary variations of temperature, 
the error will not exceed o.i on the total solids 
and less on the fat. The pipet should have a 
rather wide opening so that no cream will be 
retained. 

The Massachusetts State Board of Health has 
for many years used the routine method of 
evaporating 5 grams for two hours in a flat plati- 
num basin over boiling water. 

The A. O. A. C. method is: Heat at 100° to 
constant weight, about 3 grams in a tared plati- 
num, aluminum or tin dish of 5 cm. diameter, 
with or without the addition of 15 to 30 grams 
of sand. Cool and weigh. 

Ash. — The residue from the determination of 
total solids is heated cautiously over the Bunsen 
burner, until a white ash is left. The result 
obtained in this manner is apt to be slightly low 
from loss of sodium chlorid. This may be 
avoided by heating the residue sufficiently to 
char it, extracting the soluble matter with a few 
CO. of water, and filtering (using paper extracted 



14 MILK 

with hydrofluoric acid). The filter is added to 
the residue, the whole ashed, the filtrate then 
added, and the liquid evaporated carefully to 
dryness. The ash of normal milk is about 0.7% 
and faintly alkaline. A marked degree of alka- 
linity and effervescence with hydrochloric acid 
will suggest the addition of a carbonate. 

The method of the A. O. A. C. is as follows : In 
a weighed dish put 20 c.c. of milk from a weighing 
bottle; add 6 c.c. of nitric acid, evaporate to 
dryness, and burn at a low red heat till the ash 
is free from carbon. 

Fat. — Many methods for fat determination 
have been devised. The following will suffice for 
all practical work: 

Adams' Method. — This consists essentially in 
spreading the milk over absorbent paper, drying, 
and extracting the fat in an extraction apparatus ; 
the milk is distributed in an extremely thin layer, 
and by a selective action of the paper the larger 
portion of the fat is left on the surface. A 
paper, manufactured especially for this purpose 
by Schleicher & Schuell, is obtainable in strips 
of suitable size. Each of these yields to ether 
only from o.ooi to 0.002 gram of extract. 

Coils made of thick filter-paper, cut into 
strips 6 by 62 cm., are thoroughly extracted 
with ether and alcohol, or the weight of the ex- 
tract corrected by a constant obtained for the 



ANALYTIC PROCESSES 1 5 

paper. From a weighing bottle about 5 grams 
of the milk are transferred to the coil by means 
of a pipet, care being taken to keep dry the end 
of the coil held in the fingers. The coil is 
placed, dry end down, on a piece of glass and dried 
for one hour, preferably in an atmosphere of 
hydrogen; it is then transferred to an extraction 
apparatus and extracted with absolute ether, 
petroleum spirit of boiling-point about 45° or, 
better, carbon tetrachlorid. The extracted fat 
is dried and weighed. 

The above procedure is very satisfactory, but 
the drying in hydrogen may usually be omitted. 
After the coil has received at least twenty wash- 
ings, the flask is detached, the ether removed by 
distillation, and the fat dried by heating in an 
air-oven at about 105°, and occasionally blowing 
air through the flask. After cooling, the flask 
is wiped with a piece of silk, allowed to stand 
ten minutes, and weighed. 

Richmond states that to perform a rigidly 
accurate determination attention to the following 
points is necessary : The ether must be anhydrous 
(drying over calcium chlorid and distilling is 
sufficient). Schleicher & Schuell's fat-free papers 
should be used, and one should be extracted 
without any milk on it, as a tare for the others. 
Four or five hours' extraction is necessary, and 



l6 MILK 

the coils should be well dried before extraction is 
begun. 

Thimble-shaped cases made of fat-free paper 
are now obtainable and are convenient for holding 
the absorbent material on which the milk is 
spread. The fine texture prevents undissolved 
matter escaping. A case may be used repeatedly. 
Sour milk may be thinned with ammonium hy- 
droxid before taking the portion for analysis. 

Babcock Asbestos Method. — This is recom- 
mended by the A. 0. A. C. : Provide a hollow 
cylinder of perforated sheet metal 60 mm. long 
and 20 mm. in diameter, closed 5 mm. from one 
end by a disk of the same material. The per- 
forations should be about 0.7 mm. in diameter 
and 0.7 mm. apart. Fill the cylinder loosely with 
from 1.5 to 2.5 grams of freshly ignited woolly 
asbestos free from fine or brittle material. 
Cool in a desiccator and weigh. Introduce a 
weighed quantity of milk (about 4 grams) and 
dry at 100°. The cylinder is placed in the ex- 
traction tube and extracted with ether in the 
usual way. The ether is evaporated and the fat 
weighed. The extracted cylinder may be dried 
at 100° and the fat checked by the loss in weight. 
A higher degree of accuracy is secured by per- 
forming the drying operation in hydrogen. 

For thorough extraction, especially with diffi- 
culty soluble materials and volatile solvents, the 



ANALYTIC PROCESSES 1 7 

continuous extraction apparatus devised by 
Szombathy, but commonly called the Soxhlet 
tube, is most suitable. 

The material may be placed in a fat-free paper 
thimble and covered with a plug of cotton to 
prevent loss of fine particles. In place of the 
cotton plug, a porcelain or platinum Gooch 
crucible may be used, as shown in the cut. 
The top of the thimble should be a short dis- 
tance below, and the top of the crucible a short 
distance above, the bend of the siphon. The 
thimble should be supported by a section of 
glass tubing, i to 2 cm. long, with rounded 
edges; the edge on which the thimble rests should 
be a little uneven to prevent a close joint, which 
would hinder the siphoning of some of the 
liquid. 

Alundum cylinders will probably be useful. 

Loss of solvent by leakage often occurs. It 
may be diminished somewhat by soaking the 
corks in rather strong hot gelatin solution, 
draining them quickly and then exposing them 
for some hours to formaldehyde vapor. 

The solvents most generally employed are 
ether and petroleum spirit, but carbon tetra- 
chlorid is well adapted for extraction purposes 
as it has high solvent power for fats and is not 
easily inflammable. 

When extraction is completed, the carton and 



1 8 MILK 

materials may be removed from the tube, and, 
replacing the parts of the apparatus, much of 
the solvent may be redistilled into the extractor, 
thus recovering the liquid. Care must be taken 
not to distil the contents of the flask closely or 
heat strongly, lest some of the more volatile of 
the dissolved matters pass into the distillate. 

Roese-GoUlieh Method. — This is now being used 
for milk-products as well as for milk. For de- 
tailed description, see page 72. 

Centrifugal Methods. — Although almost all the 
fat of milk may be separated by the centrifuge, 
the emulsion is not destroyed and the volume of 
cream is merely suggestive as to the fat-content 
of the milk. To obtain a clear fatty layer in 
condition for close measurement it is necessary 
to use chemicals. The methods at present most 
employed depend essentially on one devised by 
Gustaf DeLaval, who took out a patent in Sweden 
for the use of a mixture of twenty volumes of 
strong acetic acid and one volume of strong 
sulfuric acid. This mixture coagulates and then 
dissolves the proteins, destroys the emulsion, but 
does not otherwise affect the fat and does not 
act on the lactose. By brief whirling in a cen- 
trifuge the fat collects in a clear sharply defined 
layer. DeLaval took out patents in several 
countries subsequent to the above date. 

Leffmann and Beam devised a method in which 



ANALYTIC PROCESSES 1 9 

a small amount of amyl alcohol with an equal 
volume of hydrochloric acid was added to the 
milk, and the proteins thus coagulated dissolved 
by strong sulfuric acid. About the same time 
Babcock devised a process in which sulfuric acid 
was used alone. Subsequently Gerber published 
a process in which the essential feature of the 
Leffmann-Beam method, namely, the use of amyl 
alcohol, was advised. 

The test-bottles have a capacity of about 30 c.c. 
and are provided with a graduated neck, each 
division of which represents 0.1% by weight 
of butter fat. 

15 c.c. of the milk are measured into the 
bottle, 3 c.c. of a mixture of equal parts of amyl 
alcohol and strong hydrochloric acid added, 
mixed, the bottle filled nearly to the neck with 
concentrated sulfuric acid, and the liquids mixed 
by holding the bottle by the neck and giving it a 
gyratory motion. The neck is now filled to 
about the zero point with a mixture of sulfuric 
acid and water prepared at the time. It is then 
placed in the centrifugal machine, which is so 
arranged that when at rest the bottles are in a 
vertical position. If only one test is to be made, 
the equilibrium of the machine is maintained by 
means of a test-bottle, or bottles, filled with a 
mixture of equal parts of sulfuric acid and water. 
After rotation for from one to two minutes, the 



20 MILK 

fat will collect in the neck of the bottle and the 
percentage may be read off. It is convenient to 
use a pair of dividers in making the reading. 
The legs of these are placed at the upper and lower 
limits respectively of the fat, allowance being made 
for the meniscus; one leg is then placed at the 
zero point and the reading made with the other. 
Experience by analysts in various parts of the 
world has shown that with properly graduated 
bottles the results are reliable. As a rule, they 
do not differ more than o.i % from those obtained 
by the Adams process, and are generally even 
closer. 

For great accuracy, the factor for correcting 
the reading on each of the bottles should be de- 
termined by comparison with the figures obtained 
by the Adams or other standard process. 

Cream is to be diluted to exactly ten times its 
volume, the sp. gr. taken, and the liquid treated 
as a milk. Since in the graduation of the test- 
bottles a sp. gr. of 1.030 is assumed, the reading 
must be increased in proportion. 

A more accurate result may be obtained by 
weighing in the test-bottle about 2 c.c. of the 
cream and diluting to about 15 c.c. The read- 
ing obtained is to be multiplied by 15.45 and 
divided by the weight in grams of cream taken. 

The mixture of fusel oil and hydrochloric acid 
seems to become less satisfactory when long 



ANALYTIC PROCESSES 21 

kept. It should be clear and not very dark in 
color. It is best kept in a bottle provided with a 
pipet which can be filled to the mark by dipping. 
Rigid accuracy in the measurement is not needed. 

[The Leffmann-Beam method is often erro- 
neously called the *'Beimling" method, but 
Beimling was merely the deviser of a cheap 
centrifuge. To protect the interest of a manu- 
facturer who had invested in the Beimling 
machine under the impression that it was a 
practicable method for fat estimation, it became 
necessary for Leffmann and Beam to take out a 
patent (now expired) and assign the same to this 
investor.] 

Calculation Methods. — Several investigators 
have proposed formulae by which when any two 
of the data, sp. gr., fat, and total solids, are 
known, the third can be calculated. These differ 
according to the method of analysis employed. 
That of Hehner and Richmond, as corrected 
by Richmond, was deduced from results by the 
Adams method of fat extraction. It is : 

T — 0.25 G + 1.2F + 0.14; 

in which T is the total solids, G the last two figures 
of the sp. gr. (water being looo), and F the fat. 
Patrick has proved that with American milks the 
constant should be dropped, the formula reading : 

T = 0.25 G + 1.2 F 



22 MILK 

Babcock's formula has been much used in the 
United States. It is adapted to calculating the 
solids not fat. In this formula g is the entire 
figure for sp. gr. referred to water as i. 

Snf^i ^""g-/V -x)x2.5 (100^/) 
\ioo- 1.0753 /g / ^ ' ■" 

Babcock has also given a much simpler form 
adapted for total solids. This differs but slightly 
from Richmond's. 

Total Proteins. — 3 types of processes are 
employed for this estimation: Calculation from 
the total nitrogen; precipitation and direct 
weighing ; calculation from the * ' aldehyde-figure. " 
Milk contains appreciable amounts of non- 
protein nitrogen, but the fact is usually disre- 
garded. According to Munk, this may range, in 
cow's milk, from 0.022 to 0.034%, and from 
0.014 to 0.026% in human milk. By these 
figures, the average protein nitrogen in cow's milk 
would be 94%, and in human milk 91%, of the 
total nitrogen. 

Kjeldakl-Gunning Method. — (Calculation from 
total nitrogen). 
Reagents : 

Potassium sulfate. — A coarsely powdered form 
free from nitrates and chlorids should be selected. 

Sulfuric acid. — This should have a sp. gr. 
1.84 and be free from nitrates and ammonium. 



ANALYTIC PROCESSES 23 

Standard acid. — ^/a Sulfuric or hydrochloric 
acid, the strength of which has been accurately 
determined. 

Standard alkali. — ^/lo Ammonium hydroxid, so- 
dium hydroxid, or barium hydroxid, the strength 
of which in relation to the standard acid must 
be accurately determined. 

Sodium hydroxid solution. — 500 grams should 
be added to 500 c.c. of water, the mixture al- 
lowed to stand until the undissolved matter 
settles, the clear liquor decanted and kept in a 
stoppered bottle. It will be an advantage to 
determine approximately the quantity of this 
solution required to neutralize 20 c.c. of the 
strong sulfuric acid. 

Indicator. — Cochineal solution is recommended 
by the A. O. A. C, but methyl-orange and sodium 
alizarin-monosulfonate are satisfactory. Methyl- 
orange solution should be very dilute; i part in 
1000. A drop is sufficient for 100 c.c. of liquid. 
Phenolphthalein is not well adapted to tritation 
of ammonium compounds. 

Digestion and distillation flasks. — Jena-glass 
round-bottomed flasks with a bulb 12.5 cm. 
long and 9 cm. in diameter, the neck cylindrical, 
15 cm. long and 3 cm. in diameter, flared slightly 
at the mouth. 
Process 

5 c.c. of the sample are placed in a digestion 
3 



24 MILK 

flask, lo grams of powdered potassium sulfate* 
and 15 to 25 c.c. (ordinarily about 20 c.c.) of the 
strong sulfuric acid are added and the diges- 
tion conducted as follows: The flask is placed 
in an inclined position and heated below the 
boiling-point of the acid for from five to fifteen 
minutes, or until frothing has ceased. Excessive 
frothing may be prevented by the addition of 
a small piece of paraffin. The heat is raised 
until the acid boils briskly. A small, short- 
stemmed funnel may be placed in the mouth 
of the flask to restrict the circulation of air. 
No further attention is required until the liquid 
has become clear and colorless, or not deeper 
than a pale straw. 

When Kjeldahl operations are carried out in 
limited number, the arrangement used in my 
laboratory has been found very satisfactory. A 
double- Y, terra cotta drain-pipe, about 20 cm. 
internal diameter, is connected by an elbow 
directly with the chimney-stack. The digestion 
flasks are supported as shown in the rough 
sketch, figure i (not drawn exactly to scale). 
Two flasks can be operated at once. The 
central opening is convenient for other opera- 
tions producing fumes. Openings not in use 
are closed by circles of heavy asbestos. 

Apparatus for use when many determinations 
are made are figured in the catalogs of supply- 



ANALYTIC PROCESSES 



25 



houses. As corrosive vapors are given off, it 
must be placed under a hood; but a special 
form of apparatus is now made which does not 
require an escape-pipe. 

When the liquid has become colorless or very- 
light straw yellow, it is allowed to cool, diluted 
with 100 c.c. of water if the smaller form of 




Fig. I. 



flask has been used, the liquid transferred to 
the distilling flask, and the digestion flask rinsed 
with two portions of water, 50 c.c. each, which 
are also transferred to the distilling flask. With 
the larger form of flask the dilution is made at 
once by the cautious addition of 200 c.c. of 
water. Granulated zinc, pumice stone, or 0.5 



26 MILK 

gram of zinc dust is added. 50 c.c. of the strong 
sodium hydroxid solution, or sufficient to make 
the reaction strongly alkaline, should be slowly 
poured down the side of the flask so as not to mix 
at once with the acid solution. It is convenient 
to add to the acid liquid a few drops of phenol- 
phthalein or azolitmin solution, to indicate when 
the liquid is alkaline, but it must be noted that 
strong alkaline solutions destroy the former 
indicator. The flask is shaken so as to mix the 
alkaline and acid liquids and at once attached to 
the condensing apparatus. The receiving flask 
should have been previously charged with a 
carefully measured volume of the ^/a acid (10 c.c. 
diluted with distilled water to 100 c.c. is a 
convenient amount). The distillation is con- 
ducted until about 150 c.c. have passed over. 
A small amount of indicator is added, the liquid, 
titrated with standard alkali, and the amount 
neutralized by the distilled ammonium hydroxid 
determined by subtraction. Each c.c. of ^/a 
acid neutralized is equivalent to 0.007 nitrogen. 
The nitrogen multiplied by 6.38 gives the 
total proteins. 

The distillation in this operation requires 
care, as the amount of ammonium hydroxid is 
determined by its neutralizing power, hence 
solution of the alkali of the glass will introduce 
error. Common glass is not satisfactory. Block 



ANALYTIC PROCESSES 27 

tin is a good juaterial. Moerrs found that Jena- 
glass tubes resist the action of the ammonium 
hydroxid. Distillates should be titrated promptly 
as alkali may be dissolved from the glass. 

A satisfactory condensing arrangement for 
general laboratory use is a copper tank of good 
size, through which several condensing tubes pass. 

Aldehyde Number. — The addition of formalde- 
hyde to milk increases the acidity by an action on 
the proteins. As commercial formaldehyde is 
always acid, the acidity must be either determined 
or neutralized in applying the following method. 
The application of the reaction to determination 
of proteins in milk is due to Steinegger. Rich- 
mond and Miller investigated the method and 
suggested the use of strontium hydroxid instead 
of sodium hydroxid. Richmond gives the 
following details : 

To 10 c.c. of milk at least i c.c. of a 0.5% 
solution of phenolphthalein is added and the 
liquid neutralized with standard strontium hy- 
droxid solution. To the faintly pink liquid, 2 
c.c. or more of 40% formaldehyde solution are 
added and the titration made to the same tint 
as the former. The strontium hydroxid required 
by the formaldehyde solution must be known, 
and this being deducted from that which was 
used in the titration and the remainder calculated 



28 MILK 

to c.c. ^/i acid per looo c.c. of milk will give 
the "aldehyd number." Richmond finds that 
this multiplied by 0.17 gives in most cases a close 
approximation to the total proteins obtained by 
the Kjeldahl method. 

Calculation Method. — Olson has shown that in 
normal milks the proteins may be calculated with 
close approximation by the formula 

t 
p = t- 



1-34 

in which p is protein and / total solids. 

Determination of special proteins. — 
Casein and albumin may be determined by Sebe- 
lein's method: 20 c.c. of the sample are mixed 
with 40 c.c. of a saturated solution of magnesium 
sulfate and powdered magnesium sulfate stirred 
in until no more will dissolve. The precipitate 
of casein and fat, including the trace of globulin, 
is allowed to settle, filtered, and washed several 
times with a saturated solution of magnesium 
sulfate. The filtrate and washings are saved for 
the determination of albumin. The filter and 
contents are transferred to a flask and the 
nitrogen determined by the method described 
above. The nitrogen so found, multiplied by 
6.38, gives the casein. 

The filtrate and washings from the determina- 



ANALYTIC PROCESSES 29 

tion of casein are mixed, the albumin precipitated 
by Almen's tannin reagent, filtered, and the 
nitrogen in the precipitate determined as above. 
The same factor is used. 

Almin's reagent is prepared by dissolving 4 
grams of tannin in 190 c.c. of 50% alcohol and 
adding 8 c.c. of acetic acid of 25%. 

In a mixture of milk and whey (prepared with 
rennet) in about equal parts, Richmond and 
Boseley found about 0.3% of albumoses not pre- 
cipitated by the copper sulfate nor by magnesium 
sulfate, but precipitable, along with the albumin, 
by a solution of tannin. The separation may be 
effected by diluting the filtrate from the magne- 
sium sulfate precipitation, acidifying slightly with 
acetic acid, and boiling, when the albumin will be 
coagulated and precipitated. The albumoses 
may be separated by filtering the solution and 
precipitating with tannin solution. The pre- 
cipitated proteins are best estimated by de- 
termining the nitrogen in the moist precipitate. 
The separation of the proteins may be effected, 
though less accurately, but the use of acetic acid, 
as recommended by Hoppe-Seyler and Ritt- 
hausen. 

Leffmann and Beam have modified the process 
to avoid the delay and trouble of washing the 
precipitate, as follows: 10 c.c. of the milk are 
mixed with saturated magnesium sulfate solu- 



30 MILK 

tion and the powdered salt added to saturation. 
The mixture is washed into a graduated measure 
with a small amount of the saturated solution, 
made up to loo c.c. with the same solution, 
mixed, and allowed to stand until the separation 
takes place. As much as possible of the clear 
portion is drawn off with a pipet and passed 
through a dry filter. An aliquot portion of the 
filtrate is taken, the albumin precipitated by a 
solution of tannin, and the nitrogen in the 
precipitate ascertained as above. 

The following are A. O. A. C methods: 
I. Provisional Method for the Determination of 
Casein in Cows' Milk. — The determination should 
be made when the milk is fresh. When it is not 
practicable to make the determination within 
twenty-four hours, add one part of formaldehyd 
to 2500 parts of milk and keep in a cool place. 10 
grams of the sample are diluted with about 90 c.c. 
of water at between 40° and 42°, 1.5 c.c. of a 
solution containing 10% of acetic acid by weight 
added, allowed to stand for five minutes, washed 
three times by decantation, pouring the washings 
through a filter, and the precipitate transferred 
completely to the filter. If the filtrate is not 
clear at first, it will generally become so in two 
or three filtrations, after which the washing can 
be completed. The nitrogen in the .' washed 
precipitate and filter is determined by the 



ANALYTIC PROCESSES 3 1 

Kjeldahl-Gunning method. The nitrogen, multi- 
pHed by 6.38, gives the casein. 

In working with milk which has been kept 
with preservatives, the acetic acid should be 
added in small portions, a few drops at a time with 
stirring, and the addition continued until the 
liquid above the precipitate becomes clear or 
nearly so. 

2. Provisional Method for the Determination of 
Albumin in Milk. — The filtrate obtained in the 
above operation is neutralized with sodium 
hydroxid, 0.3 c.c. of the 10% solution of acetic 
acid added, and the mixture heated for fifteen 
minutes. The precipitate is collected on a filter, 
washed, and the nitrogen determined. 

Van Slyke has pointed out that the casein can 
be approximately ascertained by multiplying 
the figure for total proteins by 0.8. 

Modified Proteins, Amino-derivatives and Am- 
monium Compounds. — The following procedures 
are given by Van Slyke. The filtrate from the 
albumin precipitate is heated to 70°, i c.c. of 
5% sulfuric acid added, then solid zinc sulfate 
to saturation. The mixture is allowed to stand 
at 70° until the caseoses settle. The liquid is 
cooled, filtered, the precipitate washed with 
saturated solution of zinc sulfate slightly acidified 
with sulfuric acid and the nitrogen ascertained 
by the Kjeldahl method. 



32 



MILK 



For amino- derivatives and ammonium com- 
pounds, 50 c.c. of the milk are mixed in a flask 
marked at 250 c.c. with i gram of sodium chlorid. 
A 1 2 % solution of tannin is added, drop by drop, 
until no further precipitation occurs. The mix- 
ture is diluted to the mark, shaken and filtered 
through a dry filter. For amino-derivatives, 50 
c.c. of the filtrate are treated for nitrogen in the 
usual way. For ammonium compounds, 100 c.c. 
of the filtrate are mixed with magnesium oxid 
and about 50 c.c. distilled, the distillate being 
received in a known volume of standard acid. 
Large excess of magnesium oxid must be avoided. 

Lactose. — For this determination, A. O. A. C. 
employs Soxhlet's method with the following 
reagents : 

Copper sulfate solution. — 34.639 grams of pure 
crystallized copper sulfate are dissolved in water 
and made up to 500 c.c. 

Alkaline tartrate solution. — 173 grams of pure 
sodium potassium tartrate and 50 grams of good 
sodium hydroxid are dissolved in water and the 
solution made up to 500 c.c. 

Sodium hydroxid /j. 

25 c.c. of the sample in a 500 c.c. flask are 
diluted with 400 c.c. of water and 10 c.c. of the 
copper sulfate solution and 8.8 c.c. ^/^ sodium 
hydroxid solution added. The mixture should 



ANALYTIC PROCESSES 33 

still have an acid reaction and contain copper in 
solution. If this is not the case, the experiment 
must be repeated, using a little less of the 
alkali. The flask is filled to the mark with water, 
shaken, and the liquid passed through a dry filter. 
50 c.c. of Fehling's solution, obtained by mixing 
equal parts of the above copper sulfate and 
alkaline tartrate solutions, are heated to brisk 
boiling in a 300 c.c. beaker, 100 c.c. of the filtrate 
obtained as above added, and boiling continued 
for six minutes ; the liquid then promptly filtered, 
and treated according to methods given below. 
The amount of lactose is calculated by the table 
on page 34 from the copper obtained by table. 
The figures for weights of copper between any 
two data given in the table may be calculated 
with sufficient accuracy for practical purposes by 
allowing 0.0008 gram of lactose for each 0.00 1 
gram of copper. 

The precipitated cuprous oxid is usually con- 
verted into free copper and weighed as such. 
Two methods may be employed for reduction: 
by hydrogen or by electrolysis. 

Reduction by Hydrogen. — The curpous oxid is 
collected on an asbestos filter. This is arranged 
most conveniently in a special filtering tube, 
which is shown in figure 2. The wider part is 
about 8 cm. and 1.5 cm. in diameter, the narrower 
portion about 5 cm. long and 0.5 cm. in caliber. 



34 



MILK 



A perforated platinum disk is sealed in just 
above the point of narrowing. The asbestos is 
placed on this disk, washed free from loose fibers, 
dried well, and the tube weighed. The filtering 
tube is attached to an exhaustion apparatus by 
passing narrower portion through the cork, and a 



Copper 


Lactose 


Copper 


Lactose 


Copper 


Lactose 


O.IOO 


0.072 


0.205 


O.151 


0.305 


0.228 


0.105 


0.075 


0.210 


0.154 


0.310 


0.232 


O.IIO 


0.079 


0.215 


0.158 


0.315 


0.236 


0.II5 


0.083 


0.220 


0.162 


0.320 


0.240 


0.120 


0.086 


0.225 


0.165 


0.325 


0.244 


0.125 


0.090 


0.230 


0.169 


0.330 


0.248 


0.130 


0.094 


0.235 


0.173 


0.335 


0.252 


0.135 


0.097 


0.240 


0.177 


0.340 


0.256 


0.140 


O.IOI 


0.245 


0,181 


0.345 


0.260 


0.145 


0.105 


0.250 


0.185 


0.350 


0.264 


0.150 


0.109 


0.255 


0.189 


0.355 


0.268 


0.155 


0.II2 


0.260 


0.192 


0.360 


0.272 


0.160 


O.II6 


0.265 


0.196 


0.365 


0.276 


0.165 


0.120 


0.270 


0.200 


0.370 


0.280 


0.170 


0.124 


0.275 


0.204 


0.375 


0.285 


0.175 


0.128 


0.280 


0.208 


0.380 


0.289 


0.180 


0.132 


0.285 


0.212 


0.385 


0.293 


0.185 


0.134 


0.290 


0.216 


0.390 


0.298 


0.190 


0.139 


0.295 


0.221 


0.395 


0.302 


0.195 


O.I4I 


0.300 


0.224 


0.400 


0.306 


0.200 


0.147 











ANALYTIC PROCESSES 35 

small funnel is fitted tightly in the top of the tube. 
The object of this funnel is to prevent the pre- 
cipitate collecting on the upper part of the tube. 
The lower end of the funnel should project several 
centimeters below the bottom of the cork through 
which it passes. 

The filtering apparatus must be arranged 
prior to the precipitation, so that the cuprous 
oxid may be filtered without delay. The pre- 
cipitate is transferred as rapidly as possible to 
the filter, well washed with hot water, alcohol, 
and ether successively, dried, and the cuprous 
oxid reduced by gentle heating in a current of 
hydrogen. When the reduction is complete, 
the heat is withdrawn, but the flow of hydrogen 
is continued until the tube is cold. It is then 
detached and weighed. 

Reduction of Copper by Electrolysis. — The fil- 
tration is performed in a Gooch crucible with 
an asbestos-felt film and the beaker in which the 
precipitation was made is well washed with 
hot water, the washings being passed through 
the filter, but it is not necessary to transfer 
all the precipitate. When the asbestos film is 
completely washed, it is transferred with the 
adhering oxid to the beaker; any oxid remaining 
in the crucible is washed into the beaker by use 
of 2 c.c. nitric acid (sp. gr. 1.42), added with a 
pipet. The crucible is rinsed with a spray of 



36 MILK 

water, the rinsings being collected in the beaker. 
The liquid is heated until all the copper is in 
solution, filtered, the filter washed until the 
filtrate amounts to at least 100 c.c, and elec- 
trolyzed. 

Electrolytic apparatus has been constructed 
in a great variety of forms. When the opera- 
tion is carried out frequently, it is best to have 
an electrolytic table. A platinum basin holding 
not less than 100 c.c. is used. A cylindrical form 
with fiat bottom is convenient. It should rest 
on a bright copper plate, which is connected 
with the negative pole of the electrical supply. 
The positive pole should be also platinum, either 
a spiral wire, cylinder, or fiat foil. Many 
operators use a funnel-shaped perforated ter- 
minal for the negative pole ; in which case a glass 
beaker or casserole will be a suitable container, 
the positive terminal being placed within the 
negative. 

Four cells of a gravity battery will suffice 
for a single decomposition, and will operate 
two, but more slowly. It is usual to arrange 
the apparatus so that the operation may be 
continued during the night. When the elec- 
tricity is taken from the general supply of the 
laboratory, it is usually necessary to interpose 
resistance and to have some means of measuring 
the current-flow. This is sometimes done with 



ANALYTIC PROCESSES 



37 



.A 



a gas evolution cell and incandescent lamp, but 
an ammeter and adjustable rheostat are better. 

Lactose may be determined by the polarim- 
eter after removal of the fat and proteins, 
which is best effected, as recommended by 
Wiley, by acid mercuric nitrate 
solution. Wiley prepared this by 
dissolving mercury in twice its 
weight of nitric acid of 1.42 sp. gr. 
and adding to the solution five vol- 
umes of water, but Revis and Bol- 
ton advise that mercuric oxid 
should be used. The A. O. A. C. 
optical method is as follows: 

For polarimeters reading to 100 
for 26.048 grams sucrose (corre- 
sponding to 32.98 grams lactose), 
measure, in c.c, the amount ob- 
tained by dividing double this (i.e., 
65.96) by the sp. gr., add 10 c.c. mercuric nitrate 
solution, make up to 102.6 c.c, shake, filter 
through a dry filter and examine in a 200 mm. 
tube. Half the observed reading will be the per- 
centage of lactose. For example, if the sp. gr. 
of the milk is 1.030, the amount taken will be 
65.90 -T- 1.030 = 64 c.c. 

The allowance for volume of precipitate by 
making up to 102.6 c.c. is not accurate, except 
with closely skimmed milks. 




38 MILK 

The correction may be made more closely by 
calculating the actual volune of the precipitate 
by multiplying the fat-percentage by 1.075 
(average specific volume of fat) and the protein- 
percentage by 0.8 (average specific volume of 
coagulated proteins), deducting the sum of these 
products from 100 c.c. and correcting the ob- 
served reading by proportion. For ordinary 
milk, the volume of the proteins from 65.96 
grams may be taken at 1.68 c.c. Supposing 
the sample to contain 4.0% of fat and the 
polarimetric reading to be 10, the calculation 
would be thus : 

65 . 96 X o . 04 = 2 . 63 Amount of fat in milk taken 
2.63 X 1 .075 = 2.82 c.c. Volume of fat in precipitate 

1 . 68 c.c. Est. vol. of proteins in precipitate 



4.50 c.c. Total volume of precipitate 
100 — 4.50 = 9 . 55 c.c. Actual volume of liquid. 
100:95-5 :: 10 19.55 9-55-^2 = 4.75, per cent, lactose. 

The employment of a factor for correcting 
for the volume of precipitate may be avoided by 
Scheibler's method of "double dilution," in 
which two solutions of different volume are 
compared. The following is a summary of the 
method given by Wiley & Ewell: For polari- 
meters adapted to a normal weight of 26.048 
sucrose, 65.82 grams of milk are placed in a 
100 c.c. flask, 10 c.c. of the acid mercuric nitrate 



ANALYTIC PROCESSES 39 

added, the flask filled to the mark, the contents 
well mixed, filtered, and a reading taken. A 
similar quantity of the milk is placed in a 200 
c.c. flask and treated in the same way. The true 
reading is obtained by dividing the product of 
the two readings by their difference. If the 
observations are made in a 200 mm. tube the 
percentage is half the true reading. 

The instrument should be accurate, and great 
care taken in the work, or the results will be less 
satisfactory than by the method first described, 
in which an allowance is made for the volume of 
the precipitate. 

Multirotation. — When freshly dissolved in cold 
water, lactose shows a higher rotation than that 
given above. By standing, or immediately on 
boiling, the rotary power falls to the point 
mentioned. In preparing solutions from the 
soHd, therefore, care must be taken to bring them 
to the boiling-point previous to making up to a 
definite volume. This precaution is unnecessary 
when operating on milk. 

Acidity. — Milk being often amphoteric to lit- 
mus, that indicator cannot be employed in 
estimating acidity. Phenolphthalein is usually 
employed. Several methods differing in details 
have been proposed. Probably the best is that 
of Thorner. In this, 10 c.c. of milk are diluted 
with 20 c.c. of water, a few drops of a dilute 
4 



40 MILK 

alcoholic solution of phenolphthalein added and 
the titration made with standard alkali. Thorner 
proposes that the number of c.c. required should 
be multiplied by lo and the result termed the 
"degree of acidity." Fresh normal milk will 
show figures ranging from i6 to i8. When the 
degree of acidity is 23 or over, the sample will 
coagulate on heating. 

The process involves a slight error, in that the 
addition of a notable amount of water to a milk 
sample disturbs somewhat the relation of the 
phosphates and diminishes the acidity. It may 
be advisable to titrate the undiluted milk. If 
the number of c.c. used is multiplied by 0.9 the 
lactic acid equivalent to the acidity of the sample 
is given in grams per 1000 c.c. 



DETECTION OF ADULTERATION 

By far the larger part of the laboratory work on 
milk is for assistance in the sanitary control of the 
supply, and the analyses are principally directed 
to the detection of the ordinary forms of adultera- 
tions. The most important of these are: skim- 
ming, watering and use of coloring, thickening 
and preserving agents. Skimming and watering 
are detected by determining fat and total solids; 
from these data the solids not fat are calculated. 
For the ordinary purposes of milk control, fat 
can be estimated with quite sufficient accuracy 
by centrifugal methods. The total solids may be 
estimated directly as described on page 12, or 
calculated from the sp. gr. and fat as indicated on 
page 21. 

Judgment whether a given sample has been 
skimmed or watered depends in many cases upon 
the standard for whole milk. Some irregularity 
of standards for fat and solids not fat exists, and 
the opinion of the analyst will be determined, 
therefore, by the standard of the locality. In 
most cases the standard for fat is between 3 and 
4%, and that for total solids about 8.50%. 

As fat diminishes the sp. gr. of milk, and the 

41 



42 MILK 

other solids increase it, it is possible to take off 
a small amount of the former and add some 
water without disturbing the sp. gr., but, of 
course, the above analytical methods will detect 
this procedure. It is now admitted that, except 
in cases of wide departure from the usual limits, 
the adulteration of milk cannot be detected by 
the sp. gr. alone but the employment of a care- 
fully graduated lactometer is of use in routine 
milk inspection. 

Direct Detection of Added Water. Serum-refrac- 
tion. — Of late years several methods have been 
proposed for this purpose but most of them have 
no positive value and have not come into general 
use. The refractive index of the whey (milk- 
serum) offers a rapid and satifactory method for 
detecting watering. Several methods of pre- 
paring this whey have been proposed, but 
Lythgoe has found, as the result of extended 
experience, the following to be satisfactory. 

Dissolve 7.25 grams of crystallized copper sulfate 
in water and dilute to 1000 c.c. If this solution 
does not refract 36 on the scale of the immersion 
refractometer at 20°, add water or copper sulfate 
until the desired result is obtained. To 8 c.c. 
of the copper solution add 32 c.c. of milk. Shake 
well and pour upon a dry filter. When the filtrate 
begins to come through clear, change the receiver, 
pour the small quantity of cloudy filtrate upon 



DETECTION OF ADULTERATION 43 

the filter and continue the filtration as usual. 
Refract the clear filtrate at 20°, by means of the 
Zeiss immersion refractometer. A reading below 
36 indicates added water. The advantages of 
this method over the acetic acid method are as 
follows: It is quicker, heating of the samples is 
unnecessary, consequently there is no error due 
to evaporation. The range of differences in the 
refraction of pure milk is less. 10% of added 
water will reduce the refraction of high-grade 
milk below the minimum, but it takes 15 % in the 
acetic acid method. Lythgoe made analyses 
of 150 samples of milk of known purity by this 
method. The total solids ranged from 17.17 to 
10.40%, the fat from 7.7 to 2.45%, the solids not 
fat from 10.50 to 7.5% and the refraction of the 
copper serum from 36.1 to 39.5. These refrac- 
tions were distributed as follows: 



Refraction 


Number 


OF Samples 


39.0 to 39.5 




6 


38.0 to 38.9 




66 


37oto37.9 




65 


36.1 to 36.9 




13 



150 

See also table of refractions on page 7 . 



As a result of extended experience, Lythgoe 
has recently given the following applications 
of some of the methods of milk analysis. 

The least variable constituents of milk are 



44 MILK 

lactose and ash, both of which are valuable data 
in detecting added water. It is possible within 
reasonable limits to indicate by the total solids 
and fat whether a given sample has been watered 
or skimmed. 

No relation exists between the refraction of 
the (sweet) serum and the ash of the sour serum 
(see page 66), therefore, if both these data are 
below those of normal milk, added water is 
positively indicated. 

The ratio of protein to fat in normal milk 
is always less than i. If the ratio exceeds i, 
skimming is indicated. If the protein-fat ratio 
is less than 0.7, or the percentage of fat to 
total solids is over 35, in samples having a low 
serum refraction, these may be declared watered, 
the refraction being not necessarily below the 
minimum for all samples of known purity. 

The sp. gr. of the sweet serum or its total 
solids may be used as a datum in place of the re- 
fraction; either will be a safe guide. 

Lowering of Freezing-point. — Several observers 
have shown that watered milk has a lower freezing- 
point than pure milk, and that the amount of 
depression has a definite relation to the amount 
of water added. One of the most recent state- 
ments on the subject is by J. W. Leather, who 
found the procedure very satisfactory for de- 
tecting watering in cows' milk and that of the 



DETECTION OF ADULTERATION 45 

India buffalo. He states that one observer 
has found that a depression to 0.537° indicates 
2.3% of added water. The procedure requires 
special apparatus and careful manipulation; data 
from testing samples of known composition should 
be obtained before relying on it in important 
cases. 

Thickening Agents. — To conceal skimming 
and watering many thickening agents have 
been used. At least two instances of the use 
of brain matter have been reported. Dextrin, 
starch, sugar, salt, gelatin and agar have all 
been used. 

Brain matter can be easily detected by the 
microscope, starch jelly by the iodin test, 
dextrin by increased polarimetric reading, sodium 
chlorid by the increased chlorids in the ash. 
Agar is frequently used in certain milk products, 
especially the cheap ice-cream sold in American 
cities. 

Gelatin. — Stokes detects the presence of gelatin 
in cream or milk as follows : 10 c.c. of the sample, 
20 c.c. of cold water, and 10 c.c. of acid mercuric 
nitrate solution (page 37) are mixed, shaken 
vigorously, allowed to stand for five minutes, 
and filtered. If much gelatin is present, it may 
be difficult to get a clear filtrate. A portion 
of the filtrate is mixed with an equal bulk 
of saturated aqueous solution of picric acid. 



46 MILK 

Gelatin produces a yellow precipitate. Picric acid 
will detect the presence of i part of gelatin in 
10,000 parts of water. The picric acid solution 
should not give a precipitate with the nitrate 
solution. 

For sucrose Cotton devised the following tests : 
10 c.c. of the sample are mixed with 0.5 gram 
of powdered ammonium molybdate, and 10 c.c. 
of dilute hydrochloric acid (i to 10) are added. 
In a second tube, 10 c.c. of pure milk or 10 c.c. 
of a 6 % solution of lactose are similarly treated. 
The tubes are then placed in the water-bath and 
the temperature gradually raised to about 80°. 
If sucrose is present, the milk will become blue, 
while genuine milk or milk-sugar remains un- 
altered unless the temperature is raised to the 
boiling-point. According to Cotton, the reaction 
is well marked in the presence of as little as i 
gram of sucrose to 1000 c.c. of the milk. For 
the detection of other organic thickening agents, 
such as pectoses, agar and mixtures of agar and 
gelatin, see under ''Cream," page 67. 

Calcium Saccharate (Saccharate of Lime). — A 
compound produced by the action of lime on 
sucrose has been used as a thickening agent. A 
test due to Bauer and Neumann is recommended 
by Ly thgoe, from whose description the following 
is taken : 

To 25 c.c. of milk (or cream) add 10 c.c. of 



DETECTION OF ADULTERATION 47 

5 % solution of uranium acetate, shake well, al- 
low to stand for five minutes and filter. To lo c.c. 
of the clear filtrate (in the case of cream use the 
total filtrate, which will be less than lo c.c.) add a 
mixture of 2 c.c. saturated ammonium molyb- 
date and 8 c.c. dilute hydrochloric acid (i part 
25% acid and 7 parts water), and place in a 
water-bath at a temperature of 80° for five minutes. 
If the sample contains sugar the solution will 
have a prussian blue tint. This should always 
be compared in a colorimeter with the standard 
Prussian blue solution prepared by adding a few 
drops of potassium ferrocyanid and 5 drops of 
10% hydrochloric acid to a solution of i c.c. of 
0.1% ferric chlorid in 20 c.c of water. 

It has been claimed that pure milk will give 
this test. Occasionally samples of pure milk will 
give a pale blue, but this can be entirely removed 
by filtration, and the filtrate will be green; while 
the color due to sucrose will pass through the 
filter, giving the blue solution characteristic of 
adulterated samples. The color is due to re- 
duction of molybdic acid, and is caused by 
levulose and dextrose as well as by sucrose. 
Solutions of I gram of lactose, levulose, dextrose 
and sucrose in 35 c.c of water were used in com- 
paring the amount of color produced when heated 
with the molybdenum reagent for five minutes. 
Lactose produced no color, levulose gave a heavy 



48 MILK 

blue, sucrose a weaker blue and dextrose the 
weakest blue, corresponding in intensity as 
lo 13 : 1. 

Stannous chlorid and ferrous sulfate give this 
color, but the reaction takes place in the cold, 
and with small quantities the color disappears on 
heating. In order for the color to persist after 
heating the sample of cream must contain these 
substances to the extent of i % calculated as the 
metal. In this case the sample will be completely 
coagulated and the taste will be disagreeable. 
Hydrogen sulfid will also give the blue, but it will 
disappear on heating. If the solution does not 
show blue before heating, it is free from hydrogen 
sulfid, ferrous sulfate or stannous chlorid. 

As a confirmatory test for sugar, the resorcinol 
test may be applied to the serum prepared with 
uranium acetate as described. This test is given 
by sucrose and levulose, but not by dextrose or 
lactose. 

The quantitative estimation of sucrose in milk 
is given under Milk Products (page 74). 

Detection of Heated Milk. — Fresh milk con- 
tains one or more enzyms of the ' ' peroxydase " 
type, that is, having power to bring about 
transfer of oxygen from peroxids to oxidable 
substances. As the function of these enzyms 
is destroyed by temperatures near 100°, it be- 
comes possible to utilize the reaction for deter- 



DETECTION OF ADULTERATION 49 

mining whether a given sample has been thus heated. 
In most cases the action of the enzym is in- 
dicated by the production of a deep blue, no 
color change occurring when the enzym has been 
heated. Hydrogen peroxid is commonly em- 
ployed for furnishing the oxygen. A considerable 
number of substances have been found to be 
susceptible to oxidation under the influence of 
the milk enzyms. Benzene derivatives, com- 
monly used as photographic developers are 
especially susceptible. Guaiacum was first used. 

Arnold's Method. — A solution of guaiacum in 
acetone is, according to Arnold and Menzel 
better than the ordinary tincture. The test is 
applied by adding to a small amount of the sample 
in a test-tube, about lo drops of the guaiacum 
solution, to which a drop or two of hydrogen 
peroxid solution has just been added, so that the 
reagent will float on the milk. If the sample 
has not been heated above 80°, the point of 
contact of the liquids will show a deep blue ring. 

As guaiacum is liable to changes both in the 
solid form and in solution it is important to de- 
termine if the reagent is sensitive to raw milk, 
hence a control test should aways be made. 
Other reagents are now available which are, in the 
main, more trustworthy. 

Dupouy's Method. — In this method, 1-4 diam- 
inobenzene is used. The reagent is dissolved in 



50 MILK 

water (a weak solution will suffice), a few drops 
added to the sample, then a few drops of hydrogen 
dioxid solution, and the liquids shaken gently. 
Milk that has not been heated above 80° gives 
immediately a bright blue. Milk that has been 
heated above this temperature shows no color 
change at first but may slowly acquire a bluish 
tint. This test is much in favor, but it is open 
to the objection that the solution of the reagent 
does not keep more than few hours, and even in 
the solid state some commercial samples soon 
decompose. 

Benzidin Method. — Wilkinson and Peters sug- 
gested this reagent, employing a solution of it 
with a few drops of acetic acid followed as usual 
by the oxidizing agent. Leffmann finds that 
the commercial benzidin hydrochlorid (furnished 
for volumetric estimation of sulfates) acts satis- 
factorily without acetic aicd. 

Wilkinson and Peters' test is performed simi- 
larly to those just described, and has a similar 
significance. They give experiments to show 
that the method is rather more delicate than 
with diamino-benzene or guaiacum. The solu- 
tion of the benzidin compound keeps better. 
They found that milk heated to 77° had lost its 
reactivity to guaiacum but retained reactivity 
to the other two reagents. Heated to 78° the 
reactivity was also lost to these. 



DETECTION OF ADULTERATION 5 1 

Leffmann has found that several commercial 
photographic developers, e. g., amidol, are ap- 
plicable in this test with about the limitations 
above noted. 

At critical temperatures, however, the results 
with all the reagents depend materially on the 
length of the heating. 

Colors. — Annatto, turmeric, and some coal-tar 
colors are much used. Caramel is occasionally 
used, saffron and carotin but rarely. Annatto 
may be detected by rendering the sample 
slightly alkaline by acid sodium carbonate, im- 
mersing a slip of filter-paper, and allowing it to 
remain over night. Annatto will cause a reddish- 
yellow stain on the paper. 

Leys gives the following method for detecting 
annatto; 50 c.c. of the sample are shaken with 
40 c.c. of 95% alcohol, 50 c.c. of ether, 3 c.c. of 
water, and 1.5 c.c. of ammonium hydroxid 
solution (sp. gr. 0.900), and allowed to stand for 
twenty minutes. The lower layer, which in pres- 
ence of annatto will be greenish-yellow, is tapped 
off and gradually treated with half its measure of 
10% solution of sodium sulfate, the separator 
being inverted without shaking, after each addi- 
tion. When the casein separates in flakes that 
gather at the surface, liquid is tapped off, strained 
through wire gauze, and placed in four test- 
tubes. To each of these amyl alcohol is added, 



52 MILK 

and the tubes shaken and immersed in cold 
water, which is gradually raised to 80°. The 
emulsion breaks up, and the alcohol, holding 
the annatto in solution, comes to the surface. 
The alcoholic layer is separated from the lower 
stratum, evaporated to dryness, and the residue 
dissolved in warm water containing a little 
alcohol and ammonium hydroxid. Clean white 
cotton is introduced and the liquid evaporated 
nearly to dryness on the water-bath. The 
cotton, which is colored a pale yellow, even with 
pure milk, is washed and immersed in a solution 
of citric acid, when it will be immediately red- 
dened if the milk contains annatto. Saffron, 
turmeric, and the coloring-matter of the marigold 
do not give a similar reaction. 

Coal-tar colors may often be detected by dyeing 
wool, but Lythgoe has devised the following 
method, which is satisfactory: 15 c.c. of the 
sample are mixed in a porcelain basin with an 
equal volume of hydrochloric acid (sp. gr. 
1.20), and the mass shaken gently so as to break 
the curd into coarse lumps. If the milk con- 
tains an azo-color, the curd will be pink; with 
normal milk the curd will be white or yellowish. 

General Method for Colors in Milk. — Leach 
devised a general method. 150 c.c. of the 
sample are coagulated in a porcelain basin, 
with the addition of acetic acid and heating, 



DETECTION OF ADULTERATION 53 

and the curd separated from the whey. The 
curd will often collect in a mass; but if this does 
not occur, it must be freed from whey by straining 
through muslin. The curd is macerated for 
several hours in a closed flask, with occasional 
shaking, with ether to extract fat. Annatto 
will also be removed by it. The ether and curd 
are separated and treated as follows: 

The ether is evaporated, the residue mixed 
with a little weak solution of sodium hydroxid, 
and passed through a wet filter; and when this 
has drained, the fat is washed off and the paper 
dried. An orange tint shows annatto, which 
may be confirmed by a drop of solution of 
stannous chlorid, which makes a pink spot. 

If the curd is colorless, no foreign coloring- 
matter is in it; if orange or brown, it should be 
shaken with strong hydrochloric acid in a test- 
tube. 

If the mass turns blue gradually, caramel is 
probably present. The whey should be ex- 
amined for caramel (see page 95). 

If the mass turns pink at once, an azo-color 
is indicated. 

Falsification of the ''Cream-line.'^ — The use of 
glass bottles for retail delivery of milk enables 
purchasers to make approximate estimations of 
the richness of the sample by the depth of cream 
formed after standing for some time, this being 



54 MILK 

of distinctly different tint from the milk below it. 
Deception has of late been extensively practised 
by a treatment of milk which breaks up the fat 
globules and increases the volume of cream 
formed, so that a slightly skimmed milk will yield 
a fair volume of cream. Determination of fat by 
the usual methods will show the fraud. See 
page 65. 

It has been found that many of the bottles 
used for distribution of milk are not of the capac- 
ity designated on them, but this is a matter of 
police regulation. 

Perservatives. — These are largely used, es- 
pecially in the warmer season, as a substitute for 
refrigeration. Many of them are sold under 
proprietary names which give no indication of 
their composition. Preparations of boric acid 
and borax were at one time the most frequent 
in use, but at present formalin, a 40% solution 
of formaldehyd, has come into favor. Sodium 
benzoate is now in common use as a preservative 
of cider, fruit- jellies, and similar articles, and 
may, therefore, be found in milk. Salicylic 
acid is not so much employed. Sodium car- 
bonate is occasionally used to prevent coagula- 
tion due to slight souring. Fluorids and abrastol 
may be used. A mixture of boric acid and borax 
is more efficient than either alone. The quantity 
generally used is equivalent to about 0.5 gram of 



DETECTION OF ADULTERATION 55 

boric acid per looo c.c. Formaldehyde is an 
efficient antiseptic. In the proportion of 0.125 
gram to 1000 c.c, it will keep milk sweet for a 
week. Hydrogen peroxid, ozone and dichro- 
mates have been used. The almost universal 
decree of sanitary authorities is that milk 
must be free from any added material, but 
owing to its comparatively high cost, liability 
to decomposition and the marked characters 
of even incipient decomposition, great tempta- 
tion to use preservatives exists and any anti- 
septic, not actively poisonous, may be used. It 
has been, found that milk drawn and marketed 
under strict sanitary precautions will keep for 
a considerable time, even at moderate tempera- 
tures. The only permissible method of pre- 
serving milk is by refrigeration. 

In addition to the descriptions of the detec- 
tion and estimation of preservatives given below, 
see also under ''Cream." 

Formaldehyde. Hehner's Test. — Hehner found 
that when milk containing formaldehyde is 
mixed with sulfuric acid containing a trace 
of a ferric compound, a distinct blue appears. 
Richmond and Boseley showed that the delicacy 
of the test is much increased if the milk is 
diluted with an equal volume of water and 
sulfuric acid of 90 to 94%, added so that it 
forms a layer underneath the milk. Under 
5 



56 MILK 

these conditions, milk, in the absence of for- 
maldehyde, gives a slight greenish tinge at 
the junction of the two liquids, while a violet 
ring is formed when formaldehyde is present 
even in so small a quantity as i part in 200,000 
of milk. The color is permanent for many 
hours. In the absence of formaldehyde, a 
brown ring may form in the course of a few 
hours, but it is below the junction line of the 
two liquids. 

Phenylhydrazin Test. — The following test 
avoids the fallacy of some other tests. A pinch 
of phenylhydrazin hydrochlorid is added to a 
few c.c. of the sample, the liquid shaken, then a 
drop of a fresh solution of sodium nitroprussid 
and a few drops of sodium hydroxid solution. 
A greenish tint is at once produced if formalde- 
hyde is present. If the test is applied to the 
liquid obtained by distilling milk the color will be 
deep blue. 

Phloroglucol Test. — A small amount of a 1% 
solution of phloroglucol is added to the sample 
and then a considerable volume of sodium 
hydroxid solution. In the presence of formalde- 
hyde a distinct rose tint will be produced. It 
is best to add the phloroglucol by means of a 
tube passed to the bottom of the test-tube. 

Bonnet's test utilizes the vapor of formalde- 
hyde, and avoids the fallacies of some of the 



DETECTION OF ADULTERATION 57 

older tests. A solution is made by dissolving 
0'035 gram pure morphin sulfate in lo c.c. of 
sulfuric acid. This solution does not keep well. 
A convenient amount of the sample is placed in 
a dish or beaker, a watch-glass containing i c.c. 
of the above solution is floated on it, and the dish 
covered with a glass plate. The materials are 
allowed to remain undisturbed at room-tempera- 
ture for several hours. Formaldehyde is in- 
dicated by the development of a color ranging 
from pink to dark blue. A black discoloration 
is disregarded. Bonnet found that with i part 
of formaldehyde to 25,000 parts of sample a 
distinct color appeared in one hour. 

In testing ice-cream and similar articles it 
must be borne in mind that some of the flavor- 
ing materials being aldehydic in nature may 
simulate formaldehyde. La Wall has found 
that vanilHn may act thus. The phenylhydrazin 
and Bonnet tests are least liable to fallacy in this 
respect. 

Nitrites and Formaldehyde. — Mixtures of these 
substances are now sold under fanciful and mis- 
leading names, for milk preservatives as a 
nitrite prevents the reactions of formaldehyde 
with some of the tests. 

Leffmann has found that the phenylhydrazin 
test will react promptly with formaldehyde in 
presence of notable amount of nitrite and also 



58 MILK 

that the well-known test for nitrites (sulfanilic 
acid and alphanaphthylamine) reacts in the 
presence of formaldehyde. The reactions are 
obtained in fresh samples and in those that have 
stood for twenty-four hours. 

Determination of Formaldehyde. — In the case 
of milk the proportion of formaldehyde is almost 
always small and it may be in great part removed 
from milk by distillation especially in a current 
of steam. B. H. Smith found that if loo c.c. 
of the sample are distilled with i c.c. of dilute 
sulfuric acid (1:3), one-third of the formaldehyde 
present will come over with the first 20 c.c. 
Distillation of milk is troublesome owing to 
bumping, but Smith found that it could be safely 
conducted with a flat evaporating burner. It is 
advisable to put a few pieces of pumice into the 
flask. 

Shrewsbury and Knapp recommend the fol- 
lowing method for estimation of formaldehyde. 
An oxidizing reagent is prepared by mixing o.i 
gram of pure nitric acid (sp. gr. 1.52) with 100 c.c. 
of strong hydrochloric acid are mixed. This 
mixture should be freshly made. 

5 c.c. of milk are treated with 10 c.c. of the 
reagent, the mixture well shaken and kept for ten 
minutes in a water-bath at 50°. The depth of 
color is proportional to the amount of formalde- 
hyde present and by means of milk containing 



DETECTION OF ADULTERATION 59 

known amounts of the preservative estimations 
may be made. 

Hydrogen Peroxid. — Many tests have been 
devised for detection of this substance. Among 
the most convenient and satisfactory is the 
reaction with vanadic acid first given by Werther. 
It may be carried out by adding to lo c.c. of the 
milk, lo drops of a i% solution of vanadic acid 
in dilute sulfuric acid. This solution may be 
conveniently made by dissolved commercial 
sodium orthovanadate in the dilute acid. 

In the presence of hydrogen peroxid a distinct 
red will appear promptly. Barthel states that a 
proportion of o.oio gram of the peroxid in loo 
c.c. of milk can be detected positively using only 
lo c.c. of the sample. 

Benzoates and Salicylates. — The following 
method covers both these preservatives. 

lo c.c. of dilute sulfuric acid (5%) are added 
to 20 c.c. of 95% alcohol and into this 50 c.c. of 
the milk are poured in a fine stream with constant 
stirring. After a few moments, the mixture is 
filtered, the filtrate being returned until it passes 
clear. A sufficient volume of the filtrate is 
extracted in the usual manner with an equal 
volume of ether or similar solvent. The solvent 
is divided into two portions that are separately 
evaporated and tested for benzoic and salicyHc 
acids respectively as given below. 



6o MILK 

Benzoates. — This is detected by a modification 
of Mohler's method by Von der Heide and 
Jakob as given by U. S. Bureau of Chemistry. 

The residue that is to be tested for benzoic 
acid is dissolved in a little water, the solution 
mixed with from i to 3 c.c. of normal sodium hy- 
droxid and evaporated to dryness. To this resi- 
due is added from 5 to 10 c.c. of concentrated sul- 
furic acid and a small crystal of potassium nitrate 
and the mixture heated either for ten minutes 
in a glycerol bath between 120° and 130° or for 
twenty minutes in boiling water. If heated in 
the glycerol bath the temperature must not be 
permitted to go over 130°. Metadinitrobenzoic 
acid is formed. After cooling i c.c. of water is 
added, the liquid made decidedly ammoniacal, 
boiled to break up ammonium nitrite, and some 
fresh colorless ammonium sulfid solution added 
so that the liquids do not mix. A brown ring at 
junction indicates benzoic acid. The liquids 
being mixed, the color diffuses and on heating 
changes to greenish-yellow. The last reaction 
distinguishes benzoic acid from salicylic and 
cinnamic acid as these latter form amino-deriva- 
tives which are not destroyed by heating. 
Phenolphthalein interferes with this process. 

Salicylic Acid. — The other portion of the 
ether-extract may be evaporated and tested for 



DETECTION OF ADULTERATION 6 1 

salicylic acid in the usual manner with a ferric 
compound. 

Saccharin. — ^A suitable amount of the sample 
(50 or 100 c.c.) is acidified with dilute (25%) 
sulfuric acid and extracted with a mixture of 
equal parts of petroleum spirit (boiling below 60°) 
and ether. The solvent is evaporated at a gentle 
heat. The presence of saccharin in the residue 
may be detected by the taste. 2 c.c. of a 
saturated solution of sodium hydroxid are added 
and the dish heated until the residue dries and 
then to 2io°-2i5°, and maintained thus for half 
an hour. The saccharin is converted into salicylic 
acid, which may be detected in the residue by 
acidulating it with sulfuric acid and applying the 
ferric chlorid test. If salicylic acid be present 
originally in the sample, the residue from the 
petroleum spirit and ether solution is dissolved 
in 50 c.c. of dilute hydrochloric acid, bromin 
water added in excess, the liquid shaken well, 
and filtered. Salicylic acid is completely removed 
as a brominated derivative. The filtrate is made 
strongly alkaline with sodium hydroxid, evapo- 
rated, and fused as described above. 

Sodium Carbonate and Sodium Acid Car- 
bonate. — These substances are occasionally added 
to milk to prevent acidity due to decomposition. 
Barthel recommends a test devised by Hilger. 
50 c.c. of the milk are diluted with 250 c.c. of 



62 MILK 

water, the mixture is heated, precipitated with a 
small amount of alcohol and a convenient 
volume filtered. The filtrate is evaporated to 
half its bulk. The presence of an alkali-carbon- 
ate is easily ascertained by the usual tests. 

Borates. — Jenkins' method is convenient and 
reasonably delicate. lo c.c. of milk are mixed 
with 7 c.c. of hydrochloric acid, filtered, a strip 
of turmeric paper dipped in the filtrate, and then 
dried on a watch-glass on the water-bath. The 
paper becomes red in the presence of borates. 

A simple test is to mix in a porcelain basin a 
drop or two of the milk, a drop of hydrochloric 
acid and a drop of alcoholic solution of turmeric 
and evaporate to dryness on the water-bath. 
The residue touched with ammonium hydroxid 
will show a distinct greenish stain in the presence 
of very small amounts of borates. 

It is obvious that the delicacy of both these 
tests may be materially increased by concen- 
trating the sample. As boric acid is volatile 
with steam it is best to render the sample slightly 
alkaline with sodium hydroxid before evaporating. 

Abrastol (Asaprol). — This is a calcium beta- 
naphthol-sulphonate that has marked antiseptic 
powers and has been used as a food preservative. 
The following test suggested by Leffmann will 
detect very small amounts. lo c.c. of the 
sample are mixed with 0.5 c.c. of the solution of 



DETECTION OF ADULTERATION 63 

mercuric nitrate described on page 37. In 
the presence of abrastol a distinct yellow tint is 
produced in a few minutes. Greater delicacy- 
can be obtained by using the same proportion 
of the reagent with 10 c.c. of milk known to be 
pure. 

Organic Contamination. — Sanitary control of 
market-milk also involves tests for animal prod- 
ucts, such as pus cells, and the identification 
of specific microbes, such as those causing tuber- 
culosis and typhoid fever. These investiga- 
tions, however, are mostly outside of the scope 
of a work on chemical analysis. For informa- 
tion concerning these recourse must be had to 
works on pathology and bacteriology. 

Several chemical tests have been published 
by which it is claimed that approximate deter- 
mination of these contaminating organisms and 
substances can be made but they are not capable 
of replacing the exact methods of the pathologic 
and bacteriologic laboratory. One of these is 
the following. A dilute solution of methylene 
blue is prepared by adding 5 c.c. of a saturated 
alcoholic solution of the dye to 200 c.c. of water. 
0.5 c.c. of this solution is added to 10 c.c. of 
the sample. If the color is discharged promptly, 
the sample contains over 100,000,000 bacteria 
per c.c. 

Hydrogen dioxid has been shown by the in- 



64 MILK 

vestigations of Rentschler to kill quickly many 
forms of microbes, and may be applicable to the 
purification of milk, when, as in war, systematic 
protection and inspection are not possible. 

Preservation of Samples. — For the preservation 
of milk samples for a day or two, refrigeration 
is the best method. Sterilization in the ordinary 
steam sterilizer used in preparing culture-media, 
will enable milk to be kept for a considerable 
time if in a flask closed with a cotton plug. 
Several preservatives have been proposed for 
keeping samples. Richmond found small amounts 
of hydrofluoric acid effective, but it has been but 
little used. Formaldehyde is very efficient; in 
large amount it increases the total solids, inter- 
feres with the reactions of the proteins and simu- 
lates some of the reactions of the carbohydrates. 
A couple of drops of commercial formalin to 25 
c.c. will preserve a sample for several days. 



MILK PRODUCTS 



CREAM 



Cream differs from whole milk principally in 
the fat-content; the analytic procedures, there- 
fore, follow those indicated under ' ' Milk, ' ' except 
that the high fat may render some modifica- 
tions advisable. It is better, for instance, to 
weigh rather than measure cream, and it is 
often advisable to dilute it with a known 
weight of water. For the determination of fat 
the Rose- Gottlieb method is much in favor 
(see page 72). The following are some special 
procedures. 

Imitation Cream. — By means of special ma- 
chinery, the fat globules of milk may be broken 
into very small portions without causing them 
to coalesce. This is termed ''homogenizing" 
and will give to poor cream an appearance of 
richness. It is also possible to incorporate 
butter with skim-milk, producing an article 
resembling cream. Of course, unsalted, un- 
colored butter must be used. As butter made 
in the usual manner, always contains water, the 

65 



66 MILK PRODUCTS 

adulteration may be detected by the change 
in the refractive power of the serum as described 
on page 42. H. C. Lythgoe, who has investi- 
gated this question, finds that samples adulter- 
ated with butter will give a refraction below 36.0. 
Results may be confirmed by taking the ash 
of the sour serum. A large amount of the 
sample is taken (as the yield of serum is small), 
soured with a pure culture of lactic acid bacillus, 
or with a little sour milk, shaken in a bottle 
until the fat and curd have separated, the serum 
drawn off and the ash of 25 c.c. taken. It 
should not be below 0.73%. The homogizing 
of cream without the addition of fat can be 
detected by microscopic examination. 

Formic Acid. — ^Revis and Bolton state that 
glucose containing this may be found in cream 
and give the following method for its detection. 

100 grams are diluted with an equal weight of 
water, 20 c.c. of a 20% solution of phosphoric 
acid added, and 100 c.c. distilled, the end of the 
condenser dipping below the surface of milk of lime 
containing at least i gram of calcium hydroxid 
and 2 c.c. of 3% acetic acid, free from formic. 
The distillate is evaporated to dryness, sealed 
in a small tube of hard glass, drawn out at one 
end that dips into a small U-tube containing 
2 c.c. of water, arranged so that none of the water 
can be drawn into the tube, and heated until 



CREAM 67 

distillation ceases. The water in the U-tube is 
mixed with 2 c.c. of Schiff's reagent. If formic 
acid was present, the mixture will become violet 
within a half hour. 

SchifE's reagent is obtained by dissolving i 
gram of rosanilin hydrochlorid in 10 c.c. of 
water, adding a mixture of 2 c.c. saturated 
solution of sodium acid sulfite and 0.5 c.c. strong 
hydrochloric acid, then water to make 100 c.c. 
The solution keeps for some time in the dark. 

j[gar. — This is now often used as a thicken- 
ing agent. Although characteristic diatoms are 
found in it, the detection of the substance by 
isolation of these has not been practically 
successful. Revis and Bolton recommend the 
following method. 

50 grams of the sample are diluted with 100 
c.c. of water, heated in boiling water and cleared 
with 5 c.c. of 10% calcium chlorid solution. 
The mixture is filtered, preferably in a hot-water 
funnel, cooled and mixed with about two-thirds 
its volume of strong alcohol. The precipitate 
(containing any agar that may have been in the 
sample) is separated, and boiled with 5 c.c. of 
water until dissolved. If it contains agar, the 
solution will gelatinize on cooHng. To detect 
the presence of gelatin in association with agar, 
the procedure is the same, except that when the 
precipitate is dissolved, a few c.c. of the solution 



68 MILK PRODUCTS 

are treated with picric acid solution. A pre- 
cipitate indicates gelatin. In this case, the re- 
mainder of the solution is evaporated to small 
bulk, and mixed with a io% solution of tannin 
until no more precipitate is produced. The 
liquid must in this treatment not have a tem- 
perature of over 60°. To it a few c.c of white of 
egg are added and the mixture heated to boiling 
for thirty minutes, filtered hot, concentrated 
to small bulk on the water and allowed to cool 
and gelatinize. 



CONDENSED MILK 

Commercial condensed milks present two prin- 
cipal forms, sweetened and unsweetened. In the 
latter sucrose is generally used. Often consti- 
tuting more than half the soUds of the product. 
Up to recent years, unsweetened condensed milk 
was largely sold in the United States as ** evapo- 
rated cream" but this is now forbidden by the 
federal food law and by many State enactments. 
Dried milk has also been manufactured but 
does not seem to have met with much favorable 
reception. Commercial evaporation of milk is 
conducted at a low temperature so that less 
modification of the ingredients is produced than 
in ordinary boiling, but some modification of the 
lactose may occur which will make polarimetric 
readings less accurate than with unheated milk. 

The analysis of unsweetened condensed milk 
can be conducted along the same lines as those 
for ordinary milk and cream, the sample being 
diluted about three times by adding a known 
volume of water. It must not be forgotten, that 
lactose may crystalHze from condensed and dried 
milks, and excessive polarimetric rotation occur in 
recently made dilutions, unless these are heated 
to brief boiling and cooled (see page 39). Com- 

69 



70 MILK PRODUCTS 

mercial condensed milks usually represent whole 
milk concentrated to about one-third or two- 
sevenths of its original volume. A small amount 
of invert-sugar may be present. The most com- 
mon defect in condensed milks is deficiency 
in fat, due to preparation from closely skimmed 
milks. Preservatives (other than sucrose) and 
coloring-matters are rarely used, nor is it likely 
that foreign fats will be present. 

The fat of unsweetened condensed milk can be 
readily determined by the L-B method (page i8). 

In a recent publication, Bigelow andPitzgerald 
give the following detailed description of the 
application of the Leffmann and Beam method 
to the examination of unsweetened condensed 
milk: 

Weigh 9 grams of evaporated milk into an 
8% Babcock milk bottle. Add lo c.c. of water. 
Thoroughly mix by shaking and add 3 c.c. of a 
mixture of equal parts of amyl alcohol and con- 
centrated hydrochloric acid. Shake thoroughly 
and add 10 c.c. of concentrated sulfuric acid 
(1.84 sp. gr.) in three or four portions, mixing 
after each addition. If too much heat develops 
the bottle may be cooled somewhat in water 
during the addition of the acid. 

Fill the bottle to near the base of the neck with 
a hot fresh mixture of equal parts of sulfuric 
acid and water. Thoroughly mix the contents 



CONDENSED MILK 7 1 

of the bottle by shaking. Raise the fat column 
to the top of the scale by means of the acid and 
water mixture, and whirl for five minutes. 
Read promptly (see page 20) from the extreme 
bottom of the fat column to the bottom of the 
upper meniscus. Multiply the reading by 2, and 
deduct 0.25; the remainder is the per cent, of 
fat. 

If an electric centrifuge without heat has been 
employed, the fat column will be somewhat cool 
and should be heated, before reading, in a water- 
bath about 60°. 

The same authors give the opinion that the 
centrifugal methods are not sufficiently accurate 
to be depended upon for determining if evapo- 
rated milk is up to standard. The Rose-Gottlieb 
method is best for this purpose. If the centrif- 
ugal methods are employed, considerable allow- 
ance must be made for inaccuracies. Results 
obtained are inaccurate unless the fat column 
is clear, with the meniscus at the bottom of the 
column perfect and not distorted by either char 
or milky appearance. 

The percentage of solids as calculated from 
the sp. gr. is not sufficiently accurate to 
determine whether the milk complies with the 
standard unless the correction factor for the for- 
mula of calculation is ascertained frequently by 
the determination of solids by drying. 

6 



72 MILK PRODUCTS 

The full analysis of sweetened condensed milk 
is difficult, and many of the published figures are 
erroneous. The sucrose interferes with the ex- 
traction of the fat by solvents. The same 
difficulty occurs in the analysis of some prepared 
infant-foods, such as mixtures of milk with malt 
and glucose. 

For the general operations, a portion of the 
well-mixed contents of a freshly opened can 
should be accurately weighed, diluted with a 
known amount of water, and well mixed, from 
which mass the portions for analysis may be 
taken and the results calculated to the original 
sample. 50 grams mixed with 150 c.c. of water 
will be a convenient quantity. For the polar- 
imetric determination of lactose, a special pro- 
cedure will be necessary ; but for determination of 
solids, ash, total proteins, and total reducing 
sugars, the examination may be made as with 
ordinary milk upon this diluted sample. 

Fat. — The Adams method is not satisfactory 
under ordinary conditions, owing to the sucrose. 
The Rose-Gottlieb method is now largely used 
and generally approved. The following descrip- 
tion is given by Bigelow and Fitzgerald : 

Weigh from 4.5 to 5.0 grams evaporated or 
condensed milk into a Rose-Gottlieb tube, add 
water to make about 11 grams and i3^ to i3^ 



CONDENSED MILK 73 

c.c. concentrated ammonium hydroxid, and thor- 
oughly mix by shaking. 

Add lo c.c. 95 % alcohol and shake thoroughly. 
Fill up to the level of the side tube with water, if 
necessary, and shake. Add 25 c.c. ether and 
shake well for one minute. Add 2 5 c.c. petroleum 
spirit (b. p. below 65°) and shake well for one 
minute. 

Allow tube to stand until layers separate 
well. Draw off ether-fat solution as completely 
as practicable and run it through a small quick- 
acting filter into a weighted flask (weighted by 
counterpoising, if the test is not finished the day 
it is started.) 

Re-extract the liquid in tube as before with 
15 c.c. of each of petroleum spirit and ether, 
shaking after each is added. Before the addition 
a little alcohol may be added and the contents 
of the tube mixed by shaking, to bring the layer 
of ammoniacal liquid close up to the outlet tube, 
for by repeated extractions the surface of sepa- 
ration is lowered. 

Run the solution from the second extraction 
through the filter into the flask, and wash end of 
spigot, filter paper, and lower surface of the 
funnel with ether; or, better, with a mixture of 
equal parts of ether and petroleum spirit which 
has been allowed to stand for separation of 
water. 



74 MILK PRODUCTS 

In the examination of cream a third extraction 
is necessary, but with evaporated and condensed 
milk the third extraction does not recover more 
than 0.02 or 0.03 % of fat, and may be omitted. 

Evaporate the liquid slowly on a steam bath 
and dry the fat in steam oven until its weight is 
constant . Weigh after one hour and then at half - 
hour intervals. As soon as the fat begins to gain 
in weight stop drying and take the next previous 
weight. Increase of weight is due to oxidation 
after all moisture and alcohol are gone. In all 
cases the drying should be completed the day it 
is begun. 

Double Extraction. — The following is given as a 
provisional A. O. A. C. m.ethod: Extract with 
ether, as usual, about 5 grams of a 40% solution, 
dry, leave the tubes in a dish containing at least 
500 c.c. of water, dry, extract again with ether for 
four hours. 

Sugars. — If regard is to be given to the 
presence of invert-sugar, a special method must 
be followed. The processes first given consider 
lactose and sucrose only. The heating employed 
in the manufacture of condensed milk may 
reduce the rotatory power of lactose sufficiently 
to cause error in the polarimetric method. The 
reducing power with alkaline copper solutions 
is not seriously affected. 

Determination of sucrose may be made by 



CONDENSED MILK 75 

difference; that is, subtracting the sum of the 
other ingredients from the total soHds. This will 
serve for ordinary inspection purposes, since 
the amount present is almost always large, gener- 
ally more than the total of milk-solids, and a 
slight error does not affect the judgment as to 
the wholesomeness of the sample. Exact work 
requires, however, that the sucrose be de- 
termined directly. Several processes have been 
devised for the purpose. Sucrose exerts but 
little action on Fehling's solution, but invert- 
sugar acts powerfully, and some processes depend 
on determining the reducing power before and 
after inversion. Since the polarimetric reading is 
also markedly changed by the inversion, the 
difference in polarization may be employed. 
Fermentation may be so conducted as to re- 
move the sucrose (also any form of glucose) while 
the lactose is unaffected. This method is chiefly 
valuable for recognizing invert-sugar or either of 
its constituents. 

Inversion Methods. — These must be such as to 
secure prompt inversion of the sucrose without 
affecting the lactose. Experiment shows that 
citric acid and invertase are the most suitable 
agents. Stokes & Bodmer have worked out the 
citric acid method substantially as follows: 

25 c.c. of the diluted sample are coagulated by 
addition of i% of citric acid, without heating, 



76 MILK PRODUCTS 

and made up to 200 c.c. plus the volume of the 
precipitated fat and proteins (see page 38). The 
liquid portion, which now measures 200 c.c, is 
passed through a dry filter. The reducing power 
with alkaline copper solutions is determined at 
once upon 50 c.c. of this filtrate. To another 
50 c.c, 1% of citric acid is added, the solution 
boiled at least thirty minutes, and the reducing 
power also determined. The increase over that 
of the first solution is due to the invert-sugar 
formed by the action of the citric acid on the 
sucrose. It is necessary to bear in mind that the 
reducing equivalents of lactose and invert-sugar 
are not the same. Volumetric methods may be 
employed. 

The following method is based on the difference 
in polarimetric reading before and after action of 
invertase. 75 cc of the diluted milk are placed 
in a loo-cc flask, diluted to about 80 c.c, 
heated to boiling, to correct birotation, cooled, 
and 10 c.c. of acid mercuric nitrate solution 
(page 37) added. The mixture is made up to 100 
cc, well shaken, filtered through a dry filter, and 
the polarimetric reading taken at once. It will 
be the sum of the effect of the two sugars. The 
volume of the sugar-containing liquid is calcu- 
lated by allowing for the precipitated proteins 
and fat, as described on page 38. 

50 c.c. of the filtrate are placed in a flask 



CONDENSED MILK 77 

marked at 55 c.c, a piece of litmus paper dropped 
in, and the excess of nitric acid cautiously neu- 
tralized by sodium hydroxid solution. The 
liquid is then faintly acidified by a single drop of 
acetic acid (it must not be alkaline), a few drops 
of an alcoholic solution of thymol are added, 
and then 2 c.c. of a solution of invertase, prepared 
by grinding half a cake of ordinary compressed 
yeast with 10 c.c. of water and filtering. The 
flask is corked and allowed to remain at a tem- 
perature of 3 5° to 40° for twenty -four hours. The 
cane-sugar will be inverted, while the milk-sugar 
will be unaffected. The flask is fllled to the mark 
(55 c.c.) with washed aluminum hydroxid and 
water, mixed, filtered, and the polarimetric 
reading taken. The amount of cane-sugar can 
be determined from the difference in the two 
readings by the formula 

^^ _ 100 a -\- b 



t 

142.08 

2 



in which 5 is the percentage of sucrose; a, the 
reading before, b, after inversion; t, the 
temperature. 

Lactose, Sucrose and Invert-sugar. — Bige- 
low and McElroy propose the following routine 
method to include invert-sugar. The reagents 
are: 



78 MILK PRODUCTS 

Acid Mercuric lodid, — Mercuric chlorid, 1.35 
grams; potassium iodid, 3.32 grams; glacial acetic 
acid, 2 c.c. ; water, 64 c.c. 

Alumina- ere am. — A cold saturated solution of 
alum is divided into two unequal portions, a 
slight excess of ammonium hydroxid is added 
to the larger portion and the remainder added 
until a faintly acid reaction to litmus is obtained. 

The entire contents of the can are transferred 
to a porcelain dish and thoroughly mixed. A 
number of portions of about 25 grams are 
weighed carefully in 100 c.c. flasks. Water is 
added to two of the portions, and the solutions 
boiled. The flasks are then cooled, clarified by 
means of a small amount of the acid mercuric 
iodid and alumina cream, made up to mark, 
filtered, and the polarimetric reading noted. 
Other portions of the milk are heated in the 
water-bath to 55°; one-half of a cake of com- 
pressed yeast is added to each flask and the 
temperature maintained at 55° for five hours. 
Acid mercuric iodid and alumina-cream are 
then added, the solution cooled to room tem- 
perature, made up to mark, mixed, filtered, and 
polarized. The amount of sucrose is determined 
by formula given above. Correction for the 
volume of precipitated solids may be made by the 
double-dilution method. The total reducing 
sugar is estimated in one of the portions by one of 



CONDENSED MILK 79 

the reducing methods, and if the sum of it and 
the amount of sucrose obtained by inversion is 
equal to that obtained by the direct reading of 
both sugars before inversion, no invert-sugar is 
present. If the amount of reducing sugar seems 
to be too great, the lactose must be re-determined 
as follows: 250 grams of the condensed milk are 
dissolved in water, the solution boiled, cooled to 
80°, a solution of about 4 grams of glacial phos- 
phoric acid added, the mixture kept at 80° for 
a few minutes, then cooled to room temperature, 
made up to mark, shaken, and filtered. It may 
be assumed that the volume of the precipitate 
is equal to that obtained by mercuric iodid solu- 
tion. Enough sodium hydroxid is then added to 
not quite neutralize the free acid, and sufficient 
water to make up for the volume of the solids 
precipitated by the phosphoric acid. The mixture 
is then filtered and the filtrate is measured in 
portions of 100 c.c. into 200-c.c. flasks. A 
solution containing 20 milligrams of potassium 
fluorid and half a cake of compressed yeast is 
added to each flask, and the mixture allowed to 
stand for ten days at a temperature between 25° 
and 30°. Invert-sugar and sucrose are fermented 
and removed by the yeast in the presence of a 
fluorid ; lactose is unaffected. The flasks are filled 
to the mark and the lactose determined either 
by reducing or by the polariscope. The amount 



8o MILK PRODUCTS 

of copper solution reduced by the lactose and 
invert-sugar, less the equivalent of lactose re- 
maining after fermentation, is due to invert- 
sugar. 



BUTTER 

Butter is a mixture of fat, water, and curd. 
The water contains lactose and the salts of the 
milk. Common salt is usually present, being 
added after the churning. Artificial coloring 
is frequently used. 

Butter-fat is distinguished from other animal 
fats in that it contains a notable proportion of 
acid radicles with a small number of carbon atoms. 
Thus, about 91% consists of palmitin and olein 
and the remainder of butyrin and caproin, along 
with small amounts of caprylin, caprin, myristin, 
and some others. According to the experiments 
of Hehner & Mitchell, stearin is present only in 
very small quantity. The exact arrangement of 
the constituents is unknown. 

The composition of good commercial butter 
usually ranges within the following limits: 

Fat 78% to 94% 

Curd i%to 3% 

Water 5% to 14% 

Salt 0% to 7% 

Butter containing over 40% of water is some- 
times sold. Such samples are pale and spongy, 
lose weight, and become rancid rapidly. 

81 



82 MILK PRODUCTS 

The official methods of the A.O.A.C. for the 
analysis of butter are as follows: 

Preparation of the Sample. — If large quantities 
of butter are to be sampled, a butter trier or 
sampler may be used. The portions thus drawn, 
about 500 grams, are to be perfectly melted in a 
closed vessel at as low a temperature as possible, 
and when melted the whole is to be shaken vio- 
lently for some minutes until the mass is homo- 
geneous and sufficiently solidified to prevent 
the separation of the water and fat. A portion 
is then poured into the vessel from which it is 
to be weighed for analysis, and should nearly or 
quite fill it. This sample should be kept in a 
cold place until analyzed. 

Water. — From 1.5 to 2.5 grams are dried to 
constant weight at the temperature of boiling 
water, in a dish with flat bottom, having a surface 
of at least 20 sq. cm. The use of clean dry sand 
or asbestos with the butter is admissible, and 
is necessary if a dish with round bottom be 
employed. 

Fat. — The dry butter from the water deter- 
mination is dissolved in the dish with absolute 
ether. The contents of the dish are then trans- 
ferred to a weighed Gooch crucible with the aid 
of a wash-bottle filled with the solvent, and are 
washed until free from fat. The crucible and 



BUTTER 83 

contents are heated at the temperature of boiling 
water till the weight is constant. 

The fat may also be determined by drying the 
butter on asbestos or sand, and extracting by 
anhydrous alcohol-free ether. After evaporation 
of the ether the extract is heated to constant 
weight at the temperature of boihng water and 
weighed. 

Casein, Ash, Chlorin. — The crucible con- 
taining the residue from the fat determination is 
covered and heated, gently at first, gradually 
raising the temperature to just below redness. 
The cover is removed and the heat continued until 
the material is white. The loss in weight rep- 
resents casein, and the residue mineral matter. 
In this mineral matter dissolved in water slightly 
acidulated with nitric acid, chlorin may be 
determined gravimetrically with silver nitrate, 
or, after neutralization with calcium carbonate, 
volumetrically, using potassium chromate as 
indicator. 

Salt. — About 10 grams are weighed in a beaker 
in portions of about i gram at a time taken from 
different parts of the sample. Hot water (about 
20 c.c.) is now added to the beaker, and after 
the butter has melted, the mass is poured into 
the bulb of a separating funnel, which is then 
closed and shaken for a few moments. After 
standing until the fat has all collected, the water 



84 MILK PRODUCTS 

is allowed to run into an Erlenmeyer flask, with 
care not to let fat globules pass. Hot water is 
again added to the beaker, and the extraction 
is repeated from ten to fifteen times, using each 
time from lo to 20 c.c. of water. The resulting 
washings contain all but a mere trace of the salt 
originally present in the butter. The chlorin is 
determined volumetrically in the filtrate by 
means of standard silver nitrate and potassium 
chromate indicator and calculated to sodium 
chlorid. 

Butter -substitutes. — The chief adulteration of 
butter consists in the substitution of foreign fats, 
especially the product known as oleomargarin. 

When fats are saponified and the soap treated 
with acid, the individual fatty acids are obtained. 
It is upon the recognition of the peculiar acid 
radicles existing in butter that the most satis- 
factory method of distinguishing it from other 
fats is based. Since the relative proportion of 
these radicles differs in different samples, the 
quantitative estimation cannot be made with 
accuracy; but when the foreign fats are substi- 
tuted to the extent of 20% or more, the adultera- 
tion an be detected with certainty and an 
approximate quantitative determination made. 

The detection of adulteration of butter-fat by 
other fats is generally carried out by the deter- 



BUTTER 85 

mination of the volatile acid, but some other 
confirmatory processes are occasionally employed. 

Qualitative Tests. — Two tests are convenient 
for preliminary examinations, especially for sort- 
ing out, when many samples are to be tested. 
The experience of Dr. William Beam and myself 
in testing many hundred samples for the Dairy 
and Food Commissioner of Pennsylvania showed 
that the methods are satisfactory and useful. 

Heating test. — When butter is heated in a 
small tin dish directly over a gas flame, it melts 
quietly, foams, and may run over the dish. 
Oleomargarin, under the same conditions, sput- 
ters noisily as soon as heated and foams but little. 
Even mixtures of butter and other fats show this 
sputtering action to a considerable extent. The 
test is not applicable to butter which has been 
melted and reworked (renovated or process 
butter) . 

Saponification test, — An alcoholic solution of 
sodium hydroxid, boiled up with butter, and then 
emptied into cold water, gives a distinct odor of 
pineapples, while oleomargarin gives only the 
alcoholic odor. 

Quantitative Methods. Volatile Acids. — 
This method, suggested by Hehner & Angell, 
systematized by Reichert, is generally called the 
Reichert process. In this form it is carried 
out by saponifying 2.5 grams of the fat, adding 



86 MILK PRODUCTS 

excess of sulfuric acid, distilling a definite portion 
of the liquid, and titrating the distillate with 
^/lo alkali. The number of c.c. of this solution 
required to overcome the acidity of the distillate 
is called the Reichert number. E. Meissl sug- 
gested the use of 5 grams, and the number so 
obtained is called the Reichert-Meissl number. 
Alcoholic solution of potassium hydroxid was 
originally used for saponification, but the solu- 
tion devised by Leffmann & Beam, namely, 
sodium hydroxid in glycerol, is more satisfactory. 
This procedure is now official in the U. S. and 
several European countries. The reagents and 
operation are as follows : 

Glycerol-soda. — 100 grams of good sodium 
hydroxid are dissolved in 100 c.c. of distilled 
water and allowed to stand until clear. 20 c.c 
of this solution are mixed with 180 c.c. of pure 
concentrated glycerol. The mixture can be con- 
veniently kept in a capped bottle holding a 10- 
c.c. pipet, with a wide outlet. 

Sulfuric Acid. — 20 c.c. of pure concentrated 
sulfuric acid, made up with distilled water to 
100 c.c. 

Sodium Hydroxid. — An approximately ^/lo, 
accurately standardized, solution of sodium 
hydroxid. 

Indicator. — Solution of phenolphthalein. 

A 300-c.c. flask is washed thoroughly, rinsed 



BUTTER 87 

with alcohol and then with ether, and thoroughly- 
dried by heating in the water-oven. After 
cooling, it is allowed to stand for about fifteen 
minutes and ' weighed. (In ordinary operation 
this preparation of the flask may be omitted.) 
A pipet, graduated to 5.75 c.c, is heated to about 
60° and filled to the mark with the well-mixed 
fat, which is then run into the- flask. After 
standing for about fifteen minutes the flask and 
contents are weighed. 20 c.c. of the glycerol- 
soda are added and the flask heated over the 
Bunsen burner. The mixture may foam some- 
what; this may be controlled, and the operation 
hastened by shaking the flask. When all the 
water has been driven off, the liquid will cease 
to boil, and if the heat and agitation be continued 
for a few moments, complete saponification will 
be effected, the mass becoming clear. The whole 
operation, exclusive of weighing the fat, requires 
about five minutes. The flask is withdrawn from 
the heat and the soap dissolved in 135 c.c. of water. 
The first portions of water should be added drop 
by drop, and the flask shaken between each 
addition in order to avoid foaming. When the 
soap is dissolved, 5 c.c. of the dilute sulfuric acid 
are added, a piece of pumice dropped in (this 
must not be omitted), and the liquid distilled 
until no c.c. have been collected. The con- 
densing tube should be of glass, and the distilla- 
7 



88 



MILK PRODUCTS 



tion conducted at such a rate that the above 
amount of distillate is collected in thirty minutes. 
The distillate is usually clear; if not, it should 
be thoroughly mixed, filtered through a dry 
filter, and loo c.c. of the filtrate taken. A little 
of the indicator is added to the distillate, and the 
standard alkali run in from a buret until neutrali- 




FiG. 3. 

zation is attained. If only 100 c.c. of the dis- 
tillate have been used for the titration, the c.c. 
of alkaU used should be increased by one-tenth. 
The distilling apparatus shown in figure 3 is 
that recommended by the A. O. A. C. (and since 
adopted in Great Britain), and the directions for 



BUTTER 89 

preparing the flask are also from the same 
source. 

When it is intended merely to distinguish 
butter from oleomargarin, it will be sufficient to 
saponify 3 c.c. of the clarified fat, dilute, acidify, 
distil 100 c.c. in the ordinary manner and titrate 
as directed. "Straight oleos," that is, samples 
containing inappreciable amounts of butter, will 
give a distillate requiring only a few c.c. of alkali. 

Butter (5 grams) yields a distillate requiring 
from 24 to 34c. c. of ^/lo alkali. Several instances 
have been published in which genuine butter has 
given a figure as low as 22.5 c.c, but such results 
are uncommon. The materials employed in 
the preparation of oleomargarin yield a distillate 
requiring less than i c.c. of alkali. Commercial 
oleomargarin is usually churned with milk in 
order to secure a butter flavor, and, thus acquiring 
a small amount of butter-fat, yields distillates 
capable of neutralizing from i to 2 c.c. of alkali. 

If coconut oil has been used in the preparation 
of the oleomargarin, the figure will be higher, but 
there will still be no difficulty in distinguishing 
pure butter. 

The determination of the Reichert number will 
usually give sufficient information as to the 
nature of a butter sample. In doubtful cases it 
may be of advantage to apply other tests as 
corroborative evidence. 



go MILK PRODUCTS 

Index of Refraction. — This datum differs nota- 
bly in different oils, but it is not of much value 
in detecting adulteration unless considerable of 
the adulterant be present. Several instruments 
have been devised for making refraction de- 
termination; a familiar one is the butyrorefrac- 
tometer of Zeiss. 

The butyrorefractometer has been strongly 
recommended for the examination of butter. 
It is equally adapted for the general examination 
of fats and oils, and may be used for the de- 
termination of the index of refraction as well. 
As these instruments are made by only one firm 
and are furnished with directions for use, further 
description will not be required. 

Renovated Butter. — So-called ''process" or 
"renovated" butter, made by melting old or in- 
ferior samples, purifying the fat, coloring and 
salting, is now a familiar article. When heated in 
a dish such butter sputters, with but little foam- 
ing as does oleomargarin, but yields with alcoholic 
solution of sodium hydroxid the pineapple odor. 
The fat or process butter gives refractometric 
data and Reichert-Meissl data similar to ordinary 
butter. Hess and Doolittle state that the curd 
of process butter has characteristic qualities, and 
propose the following method for detecting it. 

50 grams of the sample are melted in a beaker 
at about 50°. Ordinary butter yields a clear 



BUTTER 91 

fat almost as soon as melted, while with process 
butter the fat may remain turbid for a long while. 
When the curd has largely 1 settled, as much of the 
fat is poured off as possible, and the remaining 
mixture is thrown on a wet filter, by which the 
water will drain away, carrying the soluble 
proteins and salt. A few drops of acetic acid 
are added to the filtrate and the mixture is 
boiled. The filtrate from ordinary butter gives 
a slight milkiness, but that from process butter 
gives a flocculent precipitate. Quantitative ex- 
amination is made by dissolving 50 grams of the 
sample in ether; if it is ordinary butter, the curd 
is so finely divided that it remains suspended for 
some time. As much as possible of the solution 
is decanted and the mass transferred to a sepa- 
rator, the casein, water, and salt removed, and the 
remainder washed three times, at least, with 
ether to remove the fat. The curd is collected 
on a filter, washed with water, and the nitrogen 
determined by treating the precipitate with the 
filter by the Kjeldahl-Gunning method. The 
filtrate from the curd is made sHghtly acid with 
acetic acid, boiled, the precipitated proteins 
collected on a filter, and the total nitrogen de- 
termined. The factor 6.38 may be used in each 
case for converting the nitrogen into proteins. 

A distinction between ordinary and process 
butter may often be made by microscopic ex- 



92 MILK PRODUCTS 

amination under polarized light with crossed 
nicols (i. e., dark field), when the process buttet 
appears mottled, owing to the presence of 
crystals. 

Butter Colors. — Butter and butter-substitutes 
are usually artificially colored. Turmeric and 
annatto or azo-colors allied to methyl-orange are 
used. 

Azo-colors. — These may be detected by the 
test devised b}^ Geisler. A small amount of the 
sample, or, better, the fat filtered from it, is mixed 
on a porcelain plate with a little fullers' earth. 
Azo-colors give promptly a red mass; if they are 
not present, the mixture becomes only yellow or 
light brown. All samples of fullers' earth are 
not equally active, and tests should be made with 
different samples by using fat known to contain 
the azo-compound until a good specimen of the 
earth is secured. 

For the detection of very minute quantities of 
the color, the sample may be dissolved in light 
petroleum, and the fullers' earth added to the 
solution, when the pink color will appear as a 
distinct ring or zone at the edge of the deposited 
layer of the reagent. 

Low has proposed the following test for the 
yellow azo-color: A few c.c. of the filtered 
fat are mixed in a large test-tube with an 
equal volume of a mixture of one part strong 



BUTTER 93 

sulfuric acid and four parts glacial acetic acid. 
The contents of the tube are then heated almost 
to boiling and thoroughly mixed by violently 
agitating the bottom of the tube. When now 
allowed to stand and separate, the lower layer of 
mixed acids will be strongly colored wine-red if 
the azo-color be present. Pure butter-fat im- 
parts no color to the acids, or, at most, only a faint 
brownish tinge. 

Turmeric and Annatto. — Martin's test will 
usually be satisfactory: 2 c.c. carbon disulfid 
are mixed with 15 c.c. of alcohol, by adding small 
portions of the disulfid to the acohol and shaking 
gently; 5 grams of the butter-fat are added to 
this mixture in a test-tube and shaken. The 
disulfid falls to the bottom of the tube, carrying 
with it the fatty matter, while any artificial 
coloring-matter remains in the alcohol. The 
separation takes place in from one to three 
minutes. If the amount of the coloring-matter 
is small, more of the fat may be used. If the 
alcoholic solution be evaporated to dryness and 
the residue treated with concentrated sulfuric 
acid, annatto will be indicated by the production 
of a greenish-blue color. With many samples 
of oleomargarin, a pink tint will be produced, 
which indicates an azo-color. 

Palm oil has been used as a coloring agent in 
butter-substitutes. Crampton & Simons have 



94 MILK PRODUCTS 

found that two tests devised for detection of 
rosin-oil can be satisfactorily adapted to detec- 
tion of palm oil. Success depends on several 
points. The sample must be kept in a cool 
dark place until used, filtered at a temperature 
not above 70°; the heating as brief as possible, 
and promptly tested. The reagents must be 
pure and colorless. Cochran finds that annatto 
will simulate palm oil in these tests, and hence 
the absence of the former must be assured 
(see above) before inferring the presence of the 
latter. 

Halphen method. — 100 c.c. of the filtered fat 
are dissolved in 300 c.c. petroleum spirit and 
shaken out with 50 c.c. of potassium hydroxid 
solution (o. 5 % of hydroxid) . The water is drawn 
off, made distinctly acid with hydrochloric acid, 
and shaken out with 10 c.c. of carbon tetrachlorid. 
This solution is drawn off, and part of it tested 
by adding to it 2 c.c. of a mixture of i part crys- 
tallized phenol in 2 parts carbon tetrachlorid. To 
this add 5 drops of hydrobromic acid (sp. gr. 1.19). 
The test is best performed in a porcelain basin and 
the contents mixed by agitating gently. Palm oil 
gives almost immediately a bluish-green liquid. 

Liebermann-Storch method. — 10 c.c. of the 
filtered fat are shaken with an equal volume of 
acetic anhydrid, one drop of sulfuric acid (sp. 
gr. 1.53) is added and the mixture shaken for 



BUTTER 95 

a few seconds. If palm oil be present, the heavier 
layer separating will be blue with a tint of green. 

Egg-yolk has been proposed as a color for 
oleomargarin, and although its use is unlikely, 
the possibility of it should be borne in mind. 
To detect it, about lo grams of the filtered fat 
should be shaken with warm alcohol, the liquid 
drawn off as closely as possible and evaporated 
to dryness. The coloring matter of egg-yolk 
is soluble in alcohol, but insoluble in water. It 
may be distinguished from turmeric by moisten- 
ing it with a few drops of a mixture of boric and 
hydrochloric acids, and drying at a gentle heat. 
Turmeric becomes brown ; egg-color is not affected. 
Egg-yolk contains considerable lecithin, a phos- 
phoric acid derivative. Pure fats contain no 
phosphorus compound. If, therefore, a few 
grams of the fat, carefully freed from water or 
curd, are charred and the mass extracted by 
boiling with nitric acid, the filtered solution 
should not give an appreciable precipitate with 
ammonium molybdate. 

Vegetable colors may be detected by boiling 
up the filtered fat with water, drawing off the 
watery liquid, adding a few drops of hydrochloric 
acid and heating the mixture with a piece of clean, 
undyed wool. True butter colors will not dye 
wool under these circumstances. 

Caramel may be detected by shaking the 



g6 MILK PRODUCTS 

watery solution with fuller's earth and filter- 
ing. The filtrate is notably paler if caramel is 
present. Fuller's earth differs in efficiency, and 
each sample should be tested on known solutions. 

Preservatives. — The preservatives used in milk 
may be found in limited amount in butter, but a 
mixture of boric acid and borax is often added as 
a substitute for salt. 

Glucose is sometimes used as a preservative, 
especially in butter intended for export to tropical 
countries. Crampton found as much as io% 
in a sample of highly colored butter intended 
for exportation to Guadeloupe. For the de- 
tection of glucose the phenylhydrazin test might 
be used. For determination Crampton used the 
following method: lo grams of the sample were 
washed with successive portions of convenient 
bulk, the solution made up to 250 c.c, and an 
aliquot portion determined, as given for lactose 
on page 32. The solution may also be clarified 
by alumina-cream or acid mercuric nitrate and 
examined in the polarimeter. 

Boric Acid. — 25 grams of the sample are melted, 
the watery portion separated and tested as de- 
scribed on page 62. 



Cheese is the curd of milk which has been 
separated from it, pressed, and undergone some 
fermentation. The precipitation is produced 
either by allowing the milk to become sour 
— when the lactic acid is the agent — or by rennet. 
The first-named method is mainly applied to the 
manufacture of so-called Dutch or sour-milk 
cheese, green Swiss cheese, and cottage cheese. 
More commonly cheese is obtained by means of 
rennet derived from the fourth stomach of the 
calf. The action is due to an enzym which 
acts directly on the proteins and does not pro- 
duce its affect through the intervention of acids. 
The curd (cheese) undergoes, by keeping, various 
decompositions, some essentially putrefactive, 
and due to the action of microbes. The de- 
composition of the cheese is termed "ripening." 

In the sour milk cheeses, ripening is restricted 
intentionally, since there is liability to an irregular 
and miscellaneous bacterial growth by which the 
fermentations may be carried too far, undesirable 
and even harmful products being formed. Such 
cheeses are intended for prompt use. 

Cheese contains no casein, if by this term 

97 



98 MILK PRODUCTS 

is meant the protein as it exists in milk, or as 
precipitated from milk by acids. When milk 
is coagulated by rennet, only a part of the 
proteins enter into the curd; true casein contains 
about 15.7% of nitrogen, but the protein matter 
of cheese contains about 14.3%. Under the 
process of ripening this is further decomposed, 
amino- and ammonium compounds, peptones 
and albumoses being formed. 

The following figures, obtained by Van Slyke, 
will serve to give some idea of the extent to which 
the curd is changed in ripening. The figures 
represent average percentage on the total nitrogen. 
The cheese was an American cheddar: 

Green After Five 

Cheese Months 

Soluble nitrogen compounds ... 4.23 35-52 

Soluble amino compounds none 11 .66 

Soluble ammonium compounds none 2.92 

Van Slyke 's experiments seem also to indicate 
that the cheese ripened more rapidly when the 
curd was precipitated by a larger quantity of 
rennet and, especially, that cheese rich in fat 
ripened more rapidly than skim-milk cheese. 

In addition to the fat and nitrogenous com- 
pounds just mentioned, cheese may contain a 
small amount of lactose and of lactic and other 
organic acids. There is present also a certain 
proportion of mineral matter, alkaline and earthy 



CHEESE 99 

phosphates, along with any salt that has been 
added. Traces of nitrates have been found. 

Skimmed milk is not infrequently used for the 
production of cheese. Partially-skimmed milk is 
used in the preparation of certain Dutch cheeses. 
Foreign fats, such as are used in the manufacture 
of oleomargarin, are sometimes incorporated, the 
article being known as "filled cheese." 

The common American cheese is known as 
Cheddar. According to Van Slyke, this has, 
when ripe, the following average composition: 

Water 3 1 • 50% 

Fat 37-oo% 

Proteins 26.25% 

Ash, sugar, etc 5 • 25 % 

The ash of cheese consists largely of calcium 
phosphate and salt. Mariani & Tasselli de- 
termined the total ash, chlorin, calcium, and 
phosphoric acid in 15 samples of cheese. The 
amounts of salts (calculated from the chlorin) 
depend on the mode of salting. The proportion 
of phosphoric oxid was always greater than that 
necessary to form tricalcium phosphate, ranging 
from 1.07 and 1.08 equivalents of phosphoric 
anhydrid to calcium oxid in cheese made from 
sour milk to 1.56 to i in Gorgonzola, 1.67 to i 
in skim-milk cheese, and 1.75 to i in Edam cheese. 
The largest quantities of calcium and phosphoric 
oxid were found in sheep 's-milk cheese and in 



lOO MILK PRODUCTS 

cheese made from sour milk, whence it follows 
that acidity does not prevent the precipitation of 
calcium phosphate in the curds. The excess of 
phosphoric oxid obtained was attributed to acid 
phosphates. 

The salt in cheese usually ranges between i and 

4%. 

Analytic Methods. — ^The analytic points usu- 
ally determined in regard to cheese are water, fat, 
casein, ash, the presence of fats other than 
butter-fat, and coloring-matters. 

In addition to this, especially in comparing the 
qualities of genuine cheeses, the proportion of 
proteic, aminic, and ammoniacal nitrogen is of 
value. 

Care should be taken to select for analysis a 
sample which represents the average composition 
of the entire cheese. 

The following methods for the determination 
of water, fat, ash, total nitrogen, and acidity 
have been adopted by the A. O. A. C. : 

Sampling. — When the cheese can be cut, a 
narrow wedge-shaped segment, reaching from 
the outer edge to the center of the cheese, is 
taken. This is to be cut into strips and passed 
through a sausage-grinding machine three times. 
When the cheese cannot be cut, samples are taken 
by a cheese trier. If only one plug can be 
obtained, this should be perpendicular to the 



CHEESE lOI 

surface, at a point one-third of the distance from 
the edge to the center of the cheese. The plug 
should reach entirely through, or only half-way 
through, the cheese. When possible, draw three 
plugs — one from the center, one from a point 
near the outer edge, and one from a point half- 
way between the other two. For inspection 
purposes, the rind may be rejected; but for 
investigations requiring the absolute amount of 
fat in the cheese, the rind is included in the 
sample. It is preferable to grind the plugs in a 
sausage machine, but when this is not done, 
they should be cut very fine and carefully 
mixed. 

Water. — Between 2 and 5 grams of the sample 
should be placed in a weighed platinum or 
porcelain dish which contains a small amount of 
material, such as freshly ignited asbestos or sand, 
to absorb the fat that may run out. This is then 
heated in a water-oven for ten hours and weighed ; 
the loss in weight is considered as water. If 
preferred, the dish may be placed in a desiccator 
over concentrated sulfuric acid and dried to con- 
stant weight, but this may require many days. 
The acid should be renewed when the cheese 
has become nearly dry. 

Fat, — The extraction-tube described on page 16 
is prepared as follows : The perforations in the 
bottom of the tube are covered with asbestos, 



I02 MILK PRODUCTS 

on which is placed a mixture containing equal 
parts of anhydrous copper sulfate and pure dry 
sand to the depth of about 5 cm., packed loosely, 
and the upper surface covered with a film of 
asbestos. On this are placed from 2 to 5 grams 
of the sample, the mass extracted for five hours 
with anhydrous ether, then removed and ground 
to fine powder with pure sand in a mortar. The 
mixture is replaced in the extraction tube, the 
mortar washed free from all matters with ether, 
the washings being added to the tube, and the 
extraction is continued for ten hours. The fat so 
obtained is dried at 100° to constant weight. 

Here, as in most extractions, carbon tetra- 
chlorid can be substituted for ether, but the 
results obtained are not necessarily equivalent, 
and in official analyses the official method must 
be used. 

Total Nitrogen. — This is determined by the 
Kjeldahl-Gunning method, using 2 grams of the 
sample. The percentage, multiplied by 6.38, 
gives the nitrogen compounds. 

Ash. — The dry residue from the water de- 
termination may be taken for the ash. If the 
cheese is rich, the asbestos will be saturated there- 
with. This mass may be ignited carefully, and 
the fat allowed to burn off, the asbestos acting as 
a wick. No extra heating should be applied 
during the operation, as there is danger of spurt- 



CHEESE 103 

ing. When the flame has died out, the burning 
may be completed in a muffle at low redness. 
When desired, the salt may be determined in 
the ash by titration with silver nitrate and potas- 
sium chromate. 

Provisional Method for the Determination of the 
Acidity on Cheese. — Water at a temperature of 
40° is added to 10 grams of finely divided cheese 
until the volume equals 105 c.c, agitated 
vigorously, and filtered. Portions of 25 c.c. of the 
filtrate corresponding to 2.5 grams of the cheese 
are titrated with decinormal solution of sodium 
hydroxid, using phenolphthalein as indicator. 
The amount of acid is expressed as lactic acid. 

The above processes may be advantageously 
modified in some respects. The determination 
of water may be made by the extraction of the 
cheese with alcohol and ether and drying of the 
alcohol-ether extract and fat-free solids sepa- 
rately. Blyth recommends this method as more 
accurate and less tedious than the direct drying. 
In the determination of ash it will be better to 
extract the charred mass with water and pro- 
ceed as described in the determination of the ash 
of milk. 

The fat extracted by ether may be examined 

for other than butter-fat by the distillation 

method in the usual way. When the composition 

of the fat is alone desired, it may often be ex- 

8 



I04 MILK PRODUCTS 

tracted by simple methods. Pearmain & Moor 
recommend that 50 grams be chopped fine and 
tied up in a musHn bag, which is placed in a water- 
bath. When the water is heated, the fat will 
generally run out clear. If not clear, it can be 
filtered through paper. 

Henzold suggests the following: 300 grams 
of the powdered cheese are agitated in a wide- 
neck flask with 700 c.c. of 5% solution of potas- 
sium hydroxid previously warmed to 20°. In 
about ten minutes the cheese dissolves, the fat 
floats, and by cautious shaking may be col- 
lected in lumps. The liquid is diluted, the fat 
removed, washed in very cold water, keaded 
as dry as possible, melted, and filtered. It is 
claimed that the fat is not altered in composition 
by the process. 

The fat of cheese may be estimated by the 
centrifugal method, as follows: 

About 3 grams of the mixed cheese in small 
fragments are weighed and transferred to the 
bottle, the last portions being washed in with the 
acid of water. A few drops of ammonium hy- 
droxid are added, and suflicient water to make 
the liquid about 15 c.c. The liquid is warmed 
with occasional shaking until the cheese is well 
disintegrated, and then treated as a sample of 
milk. The percentage of fat is found by mul- 
tiplying the percentage reading by 15.45 and 



CHEESE 105 

dividing by the number of grams of cheese taken 
for analysis. 

Chattaway, Pearmain & Moor use the follow- 
ing modification: 2 grams of the cheese are 
placed in a small dish and heated on the water- 
bath with 30 c.c. of concentrated hydrochloric 
acid until a dark, purpHsh-colored solution is 
produced. The mixture is now poured into 
the test bottle, portions of solution remaining in 
the dish rinsed with the hydrochloric acid fusel- 
oil mixture into the bottle, and, finally, enough 
strong hot acid added to fill the bottle up to the 
mark. It is then whirled for about a minute. 
The difficulty in this method is to get all the fat 
into the bottle. It is best to weigh the cheese 
in the bottle. 

For accurate determination of fat, Revis and 
Bolton recommend the Schmid-Bondyzynski 
method, as follows: About 1.5 grams are weighed 
in a small flask, 5 c.c. of hydrochloric acid and 
a little powdered sulfur added and the mixture 
boiled gently. (For dry cheese, acid of sp. gr. 
1. 12 5 is best, for moist cheese, sp. gr. 1.19.) 
The mixture is cooled, transferred to the appara- 
tus used for Rose-GottHeb method, by the use of 
two portions of 2.5 c.c. each of alcohol and then 
small quantities of ether until 12.5 c.c. have been 
used. The contents are mixed, 12.5 c.c. light 



Io6 MILK PRODUCTS 

petroleum added and the analysis carried out 
as described on page 72. 

Lactose. — This may be estimated by boiling the 
finely divided cheese with water, filtering, and 
determining the reducing power of the filtrate 
on Fehling's solution. 

Determination oj Albuminoid Nitrogen (Stutzer's 
Method). — 0.7 to 0.8 gram of the cheese are 
placed in a beaker, heated to boiling, 2 or 3 c.c. 
of saturated alum solution added to decompose 
alkaline phosphate, then copper hydroxid mix- 
ture (see below) containing about 0.5 gram of 
the hydroxid, and stirred in thoroughly; when 
cold, the mass is filtered, washed with cold water, 
and, without removing the precipitate from the 
filter, the nitrogen determined by the Kjeldahl- 
Gunning method. Before distillation, sufficient 
potassium sulfid solution must be added to pre- 
cipitate the copper. 

The special reagent is prepared as follows: 
100 grams of copper sulfate are dissolved in 5000 
c.c. of water, 25 c.c. of glycerol added, and then 
a dilute solution of sodium hydroxid until the 
liquid is alkaline. The mass is filtered, the 
precipitate is mixed well with water containing 
5 c.c. of glycerol per liter, and washed until the 
washings are no longer alkaline. It is then 
rubbed up with a mixture of 90% water and 10% 
glycerol in sufficient quantity to obtain a uniform 



CHEESE 107 

magma that can be measured with a pipet. The 
quantity of copper hydroxid per c.c. should be 
determined. It should be kept in a well-closed 
bottle. 

Ammonium compounds. — ^About 5 grams of 
cheese are rubbed up in a mortar with water, 
transferred to a filter, and washed with a liter 
of cold water. The filtrate is concentrated by 
boiling (if alkaline, it must be neutralized before 
heating), barium carbonate added, the liquid 
distilled, and the ammonium hydroxid in 
the distillate estimated by titration with stand- 
ard acid. 

According to Stutzer, magnesium oxid or 
magnesium carbonate (the latter usually contains 
some oxid) should not be used as some of the 
amino-compounds may be decomposed. 

Amino-compounds. — The nitrogen as amino- 
compounds is estimated by subtracting from 
the figure for total nitrogen the sum of the 
protein and ammoniacal nitrogen. If nitrates 
are present, the nitrogen as such should also be 
determined and subtracted. 

Van Ketel & Antusch propose the following 
methods for estimating the nitrogen compounds: 

Ammonium compounds. — The sample, pow- 
dered with the addition of sand, is distilled with 
water and barium carbonate, and the distillate 
received in a measured quantity of standard 



I08 MILK PRODUCTS 

sulfuric acid, and, after boiling, the excess of acid 
is neutralized with standard sodium hydroxid, 
using rosolic acid as indicator. 

Amino-compounds. — These are determined by 
macerating the powdered cheese in water for 
fifteen hours at the ordinary temperature. After 
adding a little dilute sulfuric acid (1:4), the pro- 
teins and peptones are precipitated by phospho- 
tungstic acid. The precipitate is filtered off and 
washed with water containing a little sulfuric acid. 
The filtrate is made up to a definite bulk, and the 
nitrogen is determined in an aliquot portion of 
the liquid by the Kjeldahl-Gunning process, 
allowance being made for the nitrogen existing as 
ammonium. 

Peptones and Alhumoses. — These are deter- 
mined jointly by boiling the powdered cheese 
(mixed with sand as before) with water and 
filtering from the undissolved casein and albumin. 
In an aliquot portion of the filtrate the peptones 
and albumoses are precipitated by adding dilute 
sulfuric acid and phosphotungstic acid. After 
washing with acidulated water the nitrogen in 
the precipitate is determined by the Kjeldahl- 
Gunning process. 

The total nitrogen of the cheese is also deter- 
mined, and after allowing for the nitrogen ex- 
isting as other forms, the remainder is calculated 
to casein. 



CHEESE 109 

Poisonous Metals. — Lead chromate has been 
found in the rind of cheese, and finely divided 
lead in a number of Canadian cheeses. In 
England zinc sulfate has been employed under 
the name of cheese spice to prevent the heading 
and cracking. Arsenic has also been found; it 
may be detected by Reinsch's test. Lead, zinc, 
and chromium may be detected by ashing a 
portion of the sample in a porcelain crucible and 
applying the usual tests. 



FERMENTED MILK PRODUCTS 

The usual fermentation of milk is the con- 
version of the lactose into lactic acid, but by 
special methods other changes may be substituted. 
These modified fermentations are of rather 
ancient origin, and being produced by mixture 
of organisms, the products are complex and 
irregular. The proteins are more or less changed 
into proteoses and peptones. 

Kumiss is milk which has undergone alcoholic 
fermentation. The inhabitants of the steppes 
of Russia prepare it from mares' milk. When 
cows' milk is used, sucrose must be added. It 
is often made by adding sucrose and yeast to 
skim-milk. 

Vieth gives the following analysis of kumiss at 
successive stages of fermentation : 

Kumiss from Cows' Milk 

One One One Three 

Day Week Month Months 

Alcohol I.I 0.9 i.o I.I 

Solids 1 1. 3 8.9 8.6 8.5 

Fat 1.6 1.4 1.5 1.5 

Casein 2.0 2.0 1.9 1.7 

Albumin 0.3 0.2 0.2 o.i 

Carbohydrates 6.1 3.1 2.2 1.7 

Lactic acid 0.2 0.9 1.3 1.9 

Lactoprotein and peptone. 0.3 0.5 0.7 0.9 

Soluble ash o.i 0.2 0.2 0.2 

Insoluble ash 0.4 0.3 0.3 0.3 

IIO 



FERMENTED MILK PRODUCTS ill 

The item ' ' lactoprotein and peptone" refers 
to the substance precipitated by tannin after 
removal of the casein and albumin. 

Kumiss from Mares' Milk 

At the Alco- Nitrogenous Lactic Lac- 

End of: hol Fat Matters Acid tose Ash 

I day 2.47 1.08 2.25 0.64 2.210.36 

8 days 2.70 1. 13 2.00 1.16 0.690.37 

22 days 2.84 1.27 1.97 1.26 0.510.36 

Kefyr. — This is usually made from cows' milk. 
It has been used in the Caucasus for centuries. 
For its preparation a peculiar ferment is used, 
which is contained in the kefyr grains. These 
are first soaked in water, by which they are 
caused to swell and rendered more active, and 
then added to the milk. If taken out of the milk 
and dried, the grains may be used repeatedly. 

The following are analyses of kefyr: 

KONIG Hammarsten 

Alcohol o • 75 o . 72 

Fat .. 1.44 3.08 

Casein 2 . 88 2 . 94 

Albumin 0,36 o. 18 

Hemialbumose 0.26 0.07 

Peptone o . 04 

Lactose 2.41 2 . 68 

Lactic Acid i . 02 o . 73 

Ash 0.68 0.71 

According to Konig, good kefyr will not 
contain more than i % of lactic acid. 

Analytic Methods. — Solids and ash are deter- 



112 MILK PRODUCTS 

mined by evaporation as described on page 13. 
Acidity is determined by titration with ^/jo 
alkali, using phenolphthalein or methyl-orange as 
an indicator. The amount of acidity is expressed 
in terms of lactic acid. The Kjeldahl-Gunning 
method will give the total nitrogen. For further 
examination of the nitrogenous bodies, the 
methods given on pages 106 to 108 may be applied. 
Total reducing carbohydrates may be estimated 
as given on page 32. If sucrose and common 
yeast have been added, the fermented material 
will be likely to contain invert-sugar, with un- 
changed lactose and sucrose, and the method of 
examination of sweetened condensed milk may 
be applicable. Fat can, probably in all cases, 
be determined with sufficient accuracy by the 
L-B. process. If it be desired to make polari- 
metric readings, the liquid should be clarified 
with acid mercuric nitrate solution (page 37), as 
some partly hydrolyzed proteins which have 
rotatory power may not be precipitated by other 
reagents. The determination of alcohol accu- 
rately is difficult, as the quantity is usually 
small. The cautious distillation of a consider- 
able volume of the material previously neutral- 
ized with a little sodium hydroxid will yield 
a distillate in which alcohol may be detected 
and determined by the usual methods. 



FERMENTED MILK PRODUCTS II3 

Preservatives are not likely to be used, since 
they would interfere with the fermentation, but 
attempts may be made to secure better keeping 
by adding some preservative after the fermenta- 
tion has occurred. In some cases, therefore, tests 
for boric acid, formaldehyde, and salicylic acid 
should be made, as these will be most likely to be 
used. 



INDEX 



Abrastol, 62. 

Acidity, 39. . . 

Acid mercuric iodid, 78. 

nitrate, 37. 

Adams' method, 14. 
Agar, 67. 

Albumin, 2, 28, 31. 
Aldehyde number, 27. 
Almen's reagent, 29. 
Alumina-cream, 78 
Amphoteric milk, 39. 
Annatto, 51, 53, 93. 
Asaprol, 62. 
Ash, 3, 13. 

Babcock's method, 16. 
Benzoates, 59. 

Boiled milk, detection of, 48. 
Borax and boric acid, 62. 
Butter, 81. 

colors, 92. 

fat, 81. 

, process, 90. 

renovated, 90. 

Butyrorefractometer, 90. 

Calcium saccharate, 46. 

Calculation methods, 21, 28. 

Caramel, 95. 

Casein, 28, 30. 

Cheese, 97. 

Citric acid, 2. 

Colors in butter, 92. 

milk, SI. 

Colostrum, 7. 
Condensed milk, 69. 
Cream, 65. 

, evaporated, 69. 

Cryoscopy, 44. 

Egg-yolk in oleomargarin, 95. 
Enzyms in milk, 2. 
Evaporated cream, 69. 

Pat of milk, i. 
Fehling's solution, 32. 
Fermented milk, no. 
Filled cheese, 99. 
Formic acid, 66. 
Formaldehyde, 55. 
Formalin, 55. 

Gelatin, detection of, 45. 
Globulin, 2. 



Glucose, detection of, 96. 
Glycerol-soda, 86. 

Hydrogen peroxid, 59- 

Imitation cream, 65. 

Kefyr, iii. 

Kjeldahl-Gunning method, 22. 
Kumiss, no. 

Lactose, 2, 32. 

Lecithin, 3. 

LefJmann-Beam method, 19, 86. 

Mercuric iodid, acid, 78. 

nitrate, acid, 37. 

Metals in cheese, 109. 
Milk-sugar, 2, 32. 
Multirotation, 39. 

Nitrites in milk, 57. 

Oleomargarin, 84. 

Palm oil, detection of, 93. 
Preservation of samples, 64. 
Process butter, 90. 
Proteins, determination of, 22. 

Recknagel's phenomenon, 4. 
Refraction index, 42. 
Refractometer, 90. 
Reichert-Meissl number, 86. 
Renovated butter, 90. 
Roese-Gottlieb method, 72. 

Saccharin, 61. 
Saccharate of lime, 46. 
Salicylic acid, 61. 
Separated milk, 5. 
Serum-refraction, 42. 
Sodium carbonate, 61. 

benzoate, 59. 

Soxhlet's method, 32. 
Specific gravity, 8. 
Sucrose, 46, 74. 

Turmeric, 93. 

Volatile acids, 85. 



Whey, 6. 



115 



QOOOB'^ 



B55H2 # 



